Season 3 of The Diplomat arrives as the most volatile chapter yet, shifting from diplomatic maneuvers to constitutional crisis.
What began as a political negotiation has escalated into questions of power, loyalty, and national betrayal. With President Rayburn dead, Grace Penn in the Oval Office, and Kate Wyler trapped between truth and duty, every relationship is now a battlefield, professional, personal, and strategic.
This guide offers a full The Diplomat Season 3 recap, episode by episode, tracing how Kate and Hal face the consequences of secrets that can no longer be contained. From the fallout of Rayburn’s death to the discovery of a Russian nuclear weapon at sea, the season tests every alliance they thought they could rely on. What starts in diplomacy ends in open deception, even between Kate and Hal.
This article contains full spoilers for all eight episodes of The Diplomat Season 3, including major political reveals, character deaths, and the final twist involving the Poseidon torpedo. If you have not finished the season, you may want to return after watching.
Episode 1 – “Emperor Dead”
The season opens with a shock: President Rayburn collapses and dies of a heart attack at the exact moment Hal is confessing damaging truths about Vice President Grace Penn. Within hours, Grace Penn is sworn in as President of the United States.
In the chaotic aftermath, Kate confirms to Penn that Rayburn was speaking to Hal at the time of his death. The emergency swearing-in moves to the embassy, where staff scramble for symbolic essentials , a Bible, a judge, even something resembling a judicial robe, to formalize history on the fly.
Hal confronts Penn privately and warns her again: he had told the late president that she had a rogue deputy. For Hal, the oath to protect the Constitution is not ceremonial; it’s binding. Despite Billie insisting that Rayburn’s health had deteriorated for years, Hal carries guilt. Kate intervenes; if Rayburn was too fragile to hear the truth, he was no longer capable of leading.
Meanwhile, British Prime Minister Nicol Trowbridge (Rory Kinnear), ever hungry for spectacle, pushes to claim custody of Margaret Roylin. Kate blocks him, knowing what it would cost. She persuades Penn to offer asylum instead. Margaret accepts protection from Hal and Eidra, but later, unable to bear the burden, dies by suicide using her sciatica medication.
In a private moment before the oath, Penn breaks down to Kate. She believes she killed Rayburn, not Hal. Kate steadies her: it wasn’t murder, it was leadership under extreme pressure. As Vice President, Penn had been replaceable. Now as President, she must carry the consequences.
Trowbridge arrives theatrically, presenting what he claims is an authentic 1455 Gutenberg Bible. It’s also our first sight of Todd Penn (Bradley Whitford), her husband.
Later, Hal confronts Penn directly. He insists she needs Kate as Vice President. Every political misstep Penn endured came through him, not Kate. He defends his wife the only way he knows, fiercely, emotionally. He admits he doesn’t want to share her with the world, but will, if required. He ends with conviction: She cannot govern without Kate.
But Penn’s decision is a twist neither sees coming. She calls Kate and Hal, and offers the Vice Presidency not to Kate, but to Hal.
Silence. Even Hal is stunned.
Episode 2 – “Last Dance at the Country Club”
This episode weaves between past and present, showing how Kate and Hal’s marriage was built, and how it begins to fracture beyond repair.
Flashbacks: How Kate and Hal Fell in Love
We see their beginnings in 2010. Kate and Hal were in a secret relationship, hidden even from colleagues, until her mentor Carole discovered the truth. When Hal was transferred to Austria, Kate offered to follow him. He refused, not because he wanted distance, but because he refused to stall her diplomatic rise. Still, he couldn’t let her go. One night at their regular bar, Hal asked Kate to marry him.
They moved to a quiet back room. Just before entering, Hal pulled a red twist tie, the kind used to close bread bags, wrapped it into a makeshift ring, and placed it on her finger. She said yes. They kissed. It was unpolished, unceremonious, and entirely them.
In the present day, Kate still has that same red twist-tie ring.
Present Day: The Breaking Point
Kate and Hal’s bond is strained to the breaking point. Hal hasn’t yet been sworn in; he must be vetted, and already he is pushing to secure a real position for Kate. He insists she won’t be “just” Second Lady. He promises he will make it count. Kate, furious and betrayed, barely speaks to him.
Hal’s new chief of staff asks what Kate’s portfolio will be, not socially, but formally. No one offers her meaningful work. All they see is ceremonial duty.
Meanwhile, Kate prepares to leave her role as U.S. Ambassador to the United Kingdom. She shreds classified files, wipes embassy devices, signs farewell reviews, and informs the British government of her departure. Every task signals the end of a career she spent her life building.
Margaret Roylin, Eidra, and Consequences
Eidra informs Kate of Margaret Roylin’s suicide. She also warns her: if Kate leaves London entirely, Eidra will likely be dismissed as well. Yet Kate learns she is expected to return to Washington as nothing more than Second Lady. No policy seat. No diplomatic authority.
Hal negotiates directly with Billie, Chief of Staff to President Penn. He fights for Kate to receive an active role, Special Envoy to Europe, arguing that combining diplomatic authority with the public position of Second Lady could be powerful. Who would refuse a meeting requested by the Vice President’s wife? Especially with Ukraine reconstruction and NATO negotiations ahead.
This time, Kate believes him. They feel, briefly, like a team again.
Kate’s Choice
A conversation with Stuart forces her to confront what she truly wants. The Special Envoy role is vague, ambitious, but she has devoted her whole life to becoming an Ambassador. To protect Eidra, Kate takes personal responsibility before Prime Minister Trowbridge and Foreign Secretary Dennison for Margaret Roylin’s death.
In a later strategy meeting, Stuart proposes something unprecedented: what if Kate remains Ambassador to the UK while also serving as Second Lady? If she is meant to represent the modern American family, why not reflect a dual-career marriage? Why must she sacrifice everything? But the decision stands. She is expected to move to Washington. Ambassador no more.She cannot comfort Hal, because deep down, he knows it too, leaving the ambassadorship is a step down. A loss she never chose.
Airport
At the airport, Hal stands at the top of the plane’s steps. He waits. Kate does not follow. She chooses to stay in London. She remains Ambassador of the United Kingdom. Hal is left standing there, betrayed and stunned, and Kate breaks down in tears. Something inside their marriage shatters. All those flashbacks where they promised to follow each other… this time, she walks alone.
Episode 3 – “The Rideless Horse”
The episode begins just days after Kate refused to return to Washington with Hal. She arrives in D.C. for President Rayburn’s funeral, and the cold distance between them is immediate. They are careful, polite, and painfully restrained. At Blair House, they make an unspoken pact, a public marriage, private divorce. They will share a room to avoid speculation, maintain appearances, and prevent gossip. In private, though, intimacy is over. They even acknowledge the freedom to sleep with other people. Still, beneath the performed indifference, something raw lingers, love hasn’t vanished, it’s only buried under disappointment.
Hal’s Position at Risk
During preparations for the funeral, Kate notices Hal’s placement in the ceremonial lineup, pushed into the background, while the Governor of Pennsylvania stands front and center. She confronts Billie, who confirms what Kate already suspects: President Penn is considering replacing Hal with the governor. Hal’s unauthorized meetings with members of Congress, his political freelancing, and his refusal to follow her agenda have worn down Penn’s patience. She wants loyalty to Rayburn’s legacy, not independent ambition. Kate promises Billie she will rein Hal in.
Law of the Sea Treaty
That night, Kate confronts Hal about Penn’s plan to drop him. Hal doesn’t deny it. Instead, he reveals the real reason for his back-channel discussions, he’s only four Senate votes short of passing the Law of the Sea Treaty, a major international maritime agreement. Kate immediately understands: he wasn’t acting recklessly, he was maneuvering. She agrees to help him, but makes it clear, if he ever wants to be Vice President, he must stop alienating everyone around him.
Funeral Fallout
Billie outlines the rules: at the funeral, they will be seen, not heard. During the event, Kate encourages Hal to engage with the Governor of Pennsylvania, hoping to salvage his position. But when the governor suggests closing a U.S. airbase, Hal snaps. He attacks the governor publicly, arguing that while the base may not produce cutting-edge weapons, its strategic exports serve U.S. diplomacy, buying leverage, alliances, and preventing war. By humiliating the governor, Hal not only destroys the governor’s chances, he damages his own.
Kate and Penn: Brutal Honesty
After the funeral, Kate meets privately with President Penn. She’s blunt: Hal cannot be controlled. But she also insists that he is only a handful of votes away from making history with the treaty. As infuriating as he is, Hal is capable of achieving rare political success.
Meanwhile, Hal speaks with Billie. He tells her Penn cannot lead on Rayburn’s borrowed agenda. If she wants to define her presidency, she must craft her own.
Vice Presidency Confirmed
In the final moments, President Penn makes her decision. She will keep Hal, officially naming him Vice President of the United States.
As Hal walks toward the cameras, Kate steps forward and embraces him. The gesture is public, required. But the way she holds him, firm, almost desperate, is deeply personal. Their marriage is broken, but her love, complicated and painful as it is, remains.
Episode 4 – “Arden”
The Law of the Sea Treaty passes, marking a historic win, one that will carry President Penn’s name, even though Hal engineered it. But while Hal moves forward politically, Kate faces a different battle: identity.
Kate Becomes Invisible
Adjusting to life as both Ambassador and Second Lady proves harsher than she imagined. At receptions, diplomatic functions, and embassy briefings, people no longer approach her as Kate Wyler, diplomat. Instead, every conversation begins with a favor:
“Can you get me to Hal?”
Her authority dissolves. She is treated not as a policymaker, but as a gateway to her husband. It cuts deeper than politics, it strikes at her life’s work.
Protecting Eidra
To protect Eidra Park’s position as Chief of Station, Kate and Stuart devise a strategy. They propose that the London Embassy lead the Cooperative Global Messaging Initiative, a discreet alliance between MI6 and the CIA designed to signal safe passage to potential defectors, particularly those fleeing Russia. No one wants the job, which is precisely why assigning it to Eidra would secure her post.
Eidra later meets with Foreign Secretary Austin Dennison and the head of MI6. Their questions are pointed:
Did Prime Minister Trowbridge order Margaret Roylin’s death?
British intelligence wants Eidra to stay. The Prime Minister wants her gone.
Kate Cuts a Deal with Trowbridge
Kate confronts Trowbridge directly. She tells him to keep Eidra in place. He agrees, but demands a price: her endorsement of North Sea drilling. Kate weighs the consequences. To save Eidra, she accepts.
Kate and Dennison: A Moment That Fails
At a diplomatic cocktail event, Kate finds Austin Dennison. She doesn’t hide behind protocol. She tells him plainly, her marriage is over. She is open to something real with him. Their chemistry, long restrained, finally surfaces. They kiss, intensely, urgently. But Dennison pulls away.
He admits he has always felt the same way, but once again, their timing is off. Kate leaves neither as a betrayed wife nor a new lover, but as a woman suspended between duty and desire, seen by none for who she truly is.
Episode 5 – “Birdwatchers”
Five months have passed. Kate appears steadier, her movements calm and controlled. Her heightened security has eased, and she has found a rhythm in her role as Second Lady, at least publicly. Privately, everything remains fractured.
Hal’s Return and Discovery
Kate hosts a formal event at the Ambassador’s residence, a lecture led by Callum Ellis, an ornithologist and scientist. The evening is diplomatic, polished, and orderly. Then Hal arrives as a surprise for their wedding anniversary.
It takes only a glance for him to understand what has not been said aloud: Kate and Callum are involved. The realization ignites something sharp in him, anger and jealousy he cannot disguise.
The Submarine Crisis
In a private meeting, Kate, Hal, and Callum speak openly. Callum reveals who he truly is, not just an academic, but MI6. Through a Kremlin contact, he has learned that Russia has lost contact with a nuclear submarine. They cannot locate it. They cannot admit it. So MI6 has quietly approached North Sea nations, asking them to pool marine sensor data in a desperate attempt to find it. The submarine is believed to be stranded, possibly leaking radiation into coastal waters near Britain and Denmark.
The implication is catastrophic, militarily, diplomatically, environmentally.
Hal is furious. Not simply because Kate is seeing another man, but because she is now romantically entangled with someone carrying live intelligence from Russia. She has placed herself in dangerous proximity to state secrets. Kate pushes back, he chose the Vice Presidency over their marriage. For the first time all season, she breaks. She retreats to her office and cries. Not out of guilt toward Hal, but out of a deeper wound, she has hurt herself.
The Walk-In Threat
At the embassy, Eidra Park faces another crisis. “Walk-ins”, opportunists offering intelligence in exchange for visas, money, or favors, arrive constantly. Most are noise. But one stands out.
A Chechen colonel under Lenkov claims he knows the truth about the HMS Courageous attack, that America was responsible. His demand: a place for his son at Eton. Kate doesn’t dismiss it. She tells Eidra to follow it.
The Truth Breaks Open
While Kate and Hal sit for a joint interview, Eidra interrupts. The Chechen colonel has been verified. He is real military, not a fantasist. The threat is no longer rumor. Within hours, Kate, Hal, and Eidra fly to Amagansett, where President Penn is staying. Before they leave, they finally tell Eidra the truth she was never given:
The United States was responsible for the attack on the British carrier.
If the colonel speaks, everything collapses. Alliances will shatter. The world will know.
Episode 6 – “Amagansett”
In Amagansett, First Gentleman Todd Penn finally steps into full view, no longer a background observer but a critical presence in a crisis that could bring down governments.
The Unraveling Threat
A Russian colonel under Lenkov knows the truth about the HMS Courageous. He has begun speaking to the CIA. If his claims surface, the story will detonate globally, alliances will collapse, and the American cover-up will be exposed.
Kate and Hal agree on a single course: President Penn must inform Prime Minister Trowbridge and face the truth together, before it escapes their control. The source will remain protected. Grace Penn herself will not be named.
Penn’s Instinct: Confession
Grace Penn initially leans toward full disclosure. She considers admitting she colluded with Margaret Roylin as Vice President. She and Billie devise a plan, fly Trowbridge to Amagansett, confess privately, then negotiate a major trade agreement before anything is made public.
Kate immediately objects. She knows Trowbridge. He is not diplomatic. He is emotional, impulsive, and hungry for spectacle. He won’t negotiate, he’ll ignite.
Todd’s Warning and Kate’s Exclusion
Penn shares her doubts with Todd. He tells her plainly: if she confesses, she will be impeached. Kate agrees, Trowbridge will not respond with discretion, but with revenge.
Soon, Kate realizes Hal has not told Penn the full truth of his position. Billie and Penn believe Hal supports their approach, seeing strategic value in admission. Kate tells Penn directly, Hal is not aligned with this. To him, telling Trowbridge only makes sense because if it all explodes and Penn falls, he becomes President. His silence is not loyalty, it’s calculation.
Kate is quickly pushed out of the inner circle.
Hal defends himself. He tells Penn he is not deceiving her, that Kate and Todd are simply struggling with being excluded from decision-making. Todd, meanwhile, moves through the estate in quiet resentment, drinking steadily, sidelined in his own marriage.
Billie confronts Kate: Hal is needed. Kate is not. She should return to London, and leave Amagansett.
Kate’s Countermove
Kate refuses. Denied official voice, she takes another path. She joins Todd in the pool, and delivers her plan for him to carry to Grace.
Solution: blame the dead, lay responsibility at the feet of the late President Rayburn. Margaret Roylin is gone. Rayburn is gone. The administration lives.
Todd, unexpectedly lucid, understands. Hal eventually concedes. As brutal as it is, blaming Rayburn could contain the fallout. It is survival.
But personally, Hal and Kate are at their lowest. She exposed him publicly before the sitting President. Trust between them lies in pieces.
Trowbridge Arrives
With Prime Minister Trowbridge and Foreign Secretary Austin Dennison now at Amagansett, Eidra presents the consolidated intelligence. President Penn delivers the revised narrative: Margaret Roylin orchestrated the attack following a private exchange with President Rayburn.
It is a strategic fiction, stitched from fragments of truth.
A press conference is prepared. Trowbridge will receive credit for the investigation. Margaret’s name will carry the guilt. But as they start their press conference, Trowbridge does exactly what Kate predicted. He abandons the script and places full blame on former President Rayburn.
Episode 7 – “PNG”
The diplomatic fallout reaches a breaking point. In Washington, President Penn’s Cabinet demands a public apology. Hal refuses. From his perspective, using Rayburn’s name was meant to control the narrative, and it still can. Billie disagrees. Penn doesn’t need a real apology, just the appearance of one, to calm international outrage. Germany is furious. Global markets are shaking. And yet, it won’t be Penn giving the speech. It will be Kate.
Washington’s Strategy and London’s Unrest
The White House prepares an olive branch for the UK: acknowledge emotional missteps, place blame on Margaret Roylin, and deescalate. If Britain refuses, the U.S. will go further, accusing Prime Minister Trowbridge of covering for Margaret.
In London, protests swell outside the Ambassador’s residence. Kate is instructed to remain inside for safety. Callum gains entry with urgent news: the missing Russian submarine has been located, just off the British coast. But the British refuse American assistance, they intend to manage it alone, despite lacking the technology. Callum adds another warning: Trowbridge is personally fixated on Kate. She should use it.
Apology vs Power
Kate initially agrees with Hal, a U.S. apology would project weakness. But Callum offers a different reading: Trowbridge doesn’t respond to dominance. He responds to respect. A direct phone call, a gesture of humility, may prevent further escalation.
Then Kate learns the pivotal detail, Trowbridge has refused all U.S. diplomatic meetings and added a discreet appointment with a Chinese official. He is preparing to go to China for help with the submarine. Everything changes. Kate reverses course. Penn must apologize fully, directly, and without condition.
Billie objects. She believes Trowbridge is bluffing. But then Callum reveals the final, devastating truth:
The submarine carries the Poseidon torpedo, a “salted bomb,” engineered for catastrophic radioactive fallout. They once believed it was never operational. They were wrong. Kate calls Hal and Billie. For the first time, all three agree: Penn cannot signal regret. She must prostrate herself. This is no longer diplomacy; it is the prevention of a global disaster.
Callum’s Secret
Afterward, Hal quietly asks Kate how long Callum has known about Poseidon. She discovers the truth, he had known for two months, and chose silence. He gambled that if the Russians found the submarine before anyone else and tried to move it, it would not detonate. It was a calculated risk that could have ended the world.
Kate is shaken. Callum has the same dangerous arrogance she has fought in Hal, the belief in being the exception to the rules of consequence. Later, she apologizes to Callum, not for accusing him, but for carrying the broken pieces of her marriage into whatever they are. She says she wants to try. But she will need time.
Episode 8 – “Schrödinger’s Wife”
The final episode gathers all principal players at Chequers, the British Prime Minister’s country estate, President Grace Penn and her husband Todd, Kate, Hal, Prime Minister Trowbridge, his wife, and Foreign Secretary Austin Dennison with his wife, all under one roof, in one last attempt to prevent diplomatic collapse.
Tensions at Chequers
Hal immediately requests a separate room, pretending to be unwell, a move designed to avoid sharing space with Kate, or causing complications with Callum, who is also present. Kate remains distant, but Hal is careful, determined not to display jealousy.
In a quiet moment, Todd confronts Grace. He asks if her connection with Hal is more than professional. She denies it. He doesn’t believe her. He has seen the way she reacts to him, the laughter, the ease.
Grace, meanwhile, refuses to accept responsibility for Rayburn’s actions, but insists she will not abandon cooperation with the UK. In private, she tells Trowbridge the truth: the Poseidon torpedo is aboard the missing Russian submarine. She offers U.S. equipment to retrieve it safely. Trowbridge rejects her outright. He refuses to believe Poseidon is real. He refuses American help. Kate urges Callum to come clean to his Prime Minister. He refuses, admitting it would end his career.
Dinner on Diplomatic Ice
That evening, the atmosphere fractures further. Tensions spike when Todd corrects Trowbridge for confusing Heisenberg with Schrödinger’s cat, irritating both the Prime Minister and President Penn. Strangely, peace returns only when the conversation turns to Todd’s background in physics and biology, momentarily humanizing him.
Later, Callum changes his stance. He tells Kate he will speak to Trowbridge after all. Hal opposes it vehemently. Callum is the last living channel between the U.S., the UK, and Russia, losing him would sever everything. He pushes Kate: “This was your idea, why can’t you just be happy?” He claims he is trying to protect both her relationship and Callum’s position at once.
A New Strategy
Kate and Hal present an alternative: send a U.S. submarine stationed in Germany to capture photographic proof. If Poseidon is aboard, the hull will show modifications. Grace Penn resists. But later, alone with Hal, she shifts course. A plan forms, one we won’t fully understand until it is far too late.
Elsewhere, Stuart and Eidra reunite. Stuart, ready to resign and feeling betrayed by Rayburn’s attack on an ally, falters. Eidra warns him: if he seeks legal protection, his career, anywhere, is over. She tells him she wants him to stay. They kiss. They sleep together.
Back at Chequers, Todd questions Grace again. Has she ever been alone with Hal, without Billie? She denies it, irritation growing. His suspicion lingers.
Burial at Sea
The next day, Trowbridge is shown the images. Penn claims they were taken by a drone. Kate is confused; she expected submarine confirmation, not drone surveillance, but the moment slips by.
Penn insists trust has been broken, but the U.S. still wants to help. Trowbridge refuses. He accuses America of planning to seize Poseidon. She responds that he is preparing to hand it to China. Hal signals Kate. Use the Runit Dome argument, the Marshall Islands burial precedent. He knows Trowbridge’s respect for her.
Kate delivers it:
If no nation can be trusted with this weapon, not the U.S., not Russia, not China, then it must be entombed forever beneath the sea. Buried. Forgotten. No one should possess it.
For the first time, Trowbridge yields.
Love, Loss, and Lies
Callum watches. He sees what others avoid saying aloud, the bond between Kate and Hal has never vanished. That night, Kate goes to Hal. She cries. She asks him to take her back. She apologizes and asks for forgiveness. Hal answers quietly: “I never went anywhere.” They kiss and reconcile.
The Final Realization
Before leaving Chequers, Callum pulls Kate aside. The Russians have found the submarine. Radiation is dropping. Poseidon is gone.
Todd later speaks with Kate. He asks if she is troubled by Grace and Hal’s unnerving alliance, a relationship rooted not in romance but in control. Kate says she isn’t.
Todd then reveals what Grace told him: There is no intimacy, only the quiet plotting of world domination. In that instant, Kate understands. The Russians didn’t take Poseidon.
The United States did.
She pieces it together, the Ohio-class submarine drone capable of carrying Poseidon. Hal tries to stop her. He tells her Penn would want her involved. Kate is furious, Hal used her, used her credibility, to sell a lie to Trowbridge. When Britain discovers it, they will see it as an act of war. Russia will blame Britain, and strike.
Hal orders her to tell no one. He goes to Penn: “Kate knows.”
Grace is shaken, but the cameras are waiting. It’s time for the final photo session. They need to show unity, diplomacy and composure.
Todd turns to Kate: “Nothing to worry about… right?” The camera lingers on Hal and Penn, bent heads, whispering, already deciding what happens next.
Looking Ahead
The Diplomat Season 3 closes not with resolution, but with exposure. The real twist is no longer the HMS Courageous or Margaret Roylin, it’s the revelation that the United States secretly seized the Poseidon torpedo. Grace Penn and Hal Wyler have crossed into dangerous territory, willing to let Britain and Russia shoulder the blame to protect American power.
For the first time, Kate Wyler stands entirely alone. She may have reconciled emotionally with Hal, but politically, she now understands what he and Penn are capable of, and how easily they used her credibility to support a lie.
Key Details
- Title: The Diplomat Season 3
- Format: Drama series (political thriller)
- Episodes: 8
- Release date: October 16, 2025
- Cast: Keri Russell, Rufus Sewell, David Gyasi, Ali Ahn, Rory Kinnear, Ato Essandoh, Allison Janney, Bradley Whitford, Michael McKean, Nana Mensah, Miguel Sandoval, Celia Imrie
- Creator / Showrunner: Debora Cahn
- Executive Producers: Debora Cahn, Janice Williams, Keri Russell, Alex Graves, Peter Noah, Eli Attie
- Production Companies: Netflix, Well Red Films, Anonymous Content
- Source Material: Original series created for Netflix
The Poster
