Kate Wyler is a seasoned US diplomat who spent her career working behind the scenes in war-torn regions to make the world a better place. Now she’s in the limelight as US ambassador to the United Kingdom. In Season 4, she must push harder than ever to have her recommendations heard by President Grace Penn (Janney), while simultaneously fighting for her marriage to Vice President Hal Wyler (Sewell).

“They start in this really fractured place at the beginning of the season, and they stay in the room, and they say these really shitty things to each other, and they work it out, and they fight,” says Russell of Kate and Hal’s relationship this season.  

Russell adds that intense scenes with Janney are a dream. “Oh, it’s the best, being dressed down by her,” says Russell. “As crazy and frenetic as Kate is, with all her ideas, [she’s thinking], ‘I’ve just got to get my idea across to [Grace] because it’s really important, and she just doesn’t know, and I’m just going to help her out.’ And [meanwhile] Grace is steady, just watching, like, ‘Mm-hmm. Mm-hmm.’ She’s had so much more experience, and she’s watching Kate spin out of control with judgment.”

The Americans, Cocaine Bear, Felicity

Hal Wyler is Kate’s charismatic husband and a legendary diplomat in his own right. He’s negotiated the end of wars but made a lot of enemies along the way through ruthless means. Standing outside the spotlight and letting his wife shine doesn’t come naturally to Hal, which works out well for him when President Penn chooses him as her vice president at the start of Season 3. 

When we pick up with Season 4, Hal and Grace have made “a nefarious” move involving a Russian nuclear weapon, and Kate has just discovered what they’ve done. 

“I, personally, believe that there was a very, very thorny decision to be made: what to do with this incredibly dangerous situation?” says Sewell. “They made a call. You can argue the merits morally or politically of those things, and they may clash, but all the decisions made by the world leaders enter into this arena of gray.”

While the implications of this bold plan would rattle most people, Hal isn’t most people. As The Diplomat Seasons 1 to 3 have proven, the other Ambassador Wyler always manages to land on his feet. But how will he pull off his charm offensive this time?  

Scoop, Kaleidoscope,  and The Holiday.

Meet President Grace Penn, the leader of the free world. Grace enters her role at the end of Season 2 in the most dire of positions: Her predecessor dies suddenly, she’s an ocean away from home, and the Wylers know Grace is the person who set the fatal HMS Courageous attack into motion.   

By Season 4, she’s named a VP and made some pretty audacious and risky plays as commander in chief. “Those are the decisions Grace loves to make, the ones that may seem awful, but in the end are protecting the world,” says Janney. “She becomes a little scary to everyone around her [this season] because I don’t think Grace has ever questioned her instincts at all.”

Cahn adds that this season we’re really watching Grace govern. “We’re watching her settle into and grow into the role of president, which — no matter how long you’ve been in politics, no matter how long you’ve been a vice president — just isn’t the same thing,” says the creator. “There are things that you believe you will do when you take on a role like that, which are different from what happens when you’re actually doing it. And that’s a process of discovery for her with herself and for everybody around her.” 

The West Wing, I, Tonya, Lou

The Diplomat viewers have heard about Grace’s mysterious husband, Todd Penn, since Season 1. In Season 3, they finally get to meet him, and in Season 4, they see a whole lot more of him.

“I was thrilled when I heard that Debora was interested in me doing something. I had no idea what it was, and I love the show,” Whitford — who worked with Cahn on The West Wing — says. Eventually, the Emmy-winning actor learned he would play the new first husband of the United States, reuniting him with his West Wing co-star Janney. 

Although the world is focused on Grace’s ascent to power, Todd is evolving right alongside her. “Todd is making a big adjustment in his life with not a lot of grace, enthusiasm, or warning,” Whitford says. “The thing that I love about this show is the diplomacy is always just amplified and resonating with what’s going on personally. That’s really fun. There’s a power dynamic [between Grace and Tood]. There’s negotiation.” 

The West Wing, The Madness, Death by Lightning 

Stuart Hayford is Kate’s deputy chief of mission at the US embassy in London. He’s her savvy right-hand man, nudging her in the right diplomatic directions as needed. He’s also a former DC campaign manager with deep connections in the White House. 

Essandoh says when Season 4 kicks off there’s “no room to breathe.” He adds, “We jump right back in. The domino effect of how that information [that Kate has discovered] affects not just the political discourse and the world discourse, but the personal relationships between everybody continues throughout the entire season.” 

While Kate finds herself struggling to be heard, Stuart must also make sure he speaks up this season. “I think that this has always been a balance between the Kates of the world and the Stuarts of the world,” says Essandoh. “I’ve always thought of Stuart as — maybe this is a bad word, but — idealistic. He has a vision of how things are supposed to work. So does Kate, but Kate has enough experience to know that you do have to get dirty sometimes. Stuart understands that, but there’s something about that that really puts a bad taste in his mouth.”

Chicago Med, Reptile, and Altered Carbon

Eidra Park is the chief of the CIA station in London, one of the largest CIA hubs in the world. She manages the very close, very important, and very complicated relationship between the CIA and MI6 and is responsible for relaying intelligence information to Kate’s team. While initially suspicious of Kate, she eventually warms to her.

“I talked to a couple consultants — women who used to work within the CIA and were chiefs of stations,” says Ahn on her prep for the role. “Then I read some memoirs [by] people who lived their life undercover, which were basically things that Eidra would’ve done before she got to this job.” 

Like the rest of her colleagues, Eidra must weather a continuously shifting political landscape, while also trying to prioritize her romantic relationship with Stuart. “I think her compartmentalization is catching up to her [this season],” says Ahn. “Her job makes it so that she really can’t get that close to people, she’s always moving, and so she knows that, and I think she’s been trying to protect Stuart from all of that. But the fact that Stuart just refuses to go away and because he just keeps insisting that she trust him, a softening is happening, whether she likes it or not.”

Agatha All Along, Raising Dion, Supernatural

Nicol Trowbridge is the prime minister of the United Kingdom. Foulmouthed and volatile, Trowbridge never questions his own war-hawk mentality. That’s Dennison’s (exhausting) job. After the reveal that the US was involved in the carrier attack, Trowbridge is left deeply mistrusting of the Penn administration. By the end of Season 3, amends are starting to be made between the two nations, but Trowbridge is unaware of Grace and Hal’s next move, which is potentially disastrous for the UK. 

Creator Cahn is in awe of Kinnear’s talents as Trowbridge. “Director Alex Graves calls Rory Kinnear the Stradivarius. He can do anything, and he does it at such a level of skill and excellence that it’s just mind-boggling,” Cahn says.” When Rory’s working, a lot of us sit there asking for more takes just so that we can watch him perform, like we’re at the theater or something — like we bought a ticket and now we get to see what he does over and over again.”

The Bank of Dave films, Toxic Town, Black Mirror  (as yet another prime minister)

Austin Dennison is the British foreign secretary under Prime Minister Trowbridge. Weighed down by his struggle to rein in his brash head of government, Dennison comes to rely on Kate, and they become unexpected allies — and maybe something more. But their relationship is always one dilemma away from being completely flipped on its head.  

“At the end of Season 2, Dennison’s like, ‘I want nothing more to do with you, Kate. I am second in command to this guy and my country,’” says Gyasi. “In Season 3, we pick right up where we left off.” 

But, by the end of Season 3, Dennison is a married man — seemingly making his relationship with Kate purely professional from here on …

When we pick up Season 4, Trowbridge has sent Dennison to Amritsar, India to meet with the foreign minister. 

Interstellar, Half Bad: The Bastard Son & The Devil Himself, Troy: Fall of a City 

Margaret Roylin is like political kryptonite in The Diplomat — potentially radioactive to the touch but irresistible up close. She was the prime minister’s former adviser whose shrewdness is to be envied, no matter which party you support. 

As a key figure in the planning of the HMS Courageous explosion, Roylin’s choices sent shockwaves through The Diplomat’s delicate political ecosystem. 
 

By the Season 3 premiere, Prime Minister Trowbridge knows of Roylin’s connection to the Courageous attack. In response, the United States offers Roylin asylum in America. Rather than betray her country further, Roylin tragically dies by suicide toward the close of Episode 1.

Thursday Murder Club, Good Grief, Malevolent 

This enigmatic Brit — a bit of a “bird watcher” — manages to charm Kate. When the spy brings vital information to Kate in the Season 3 finale, she starts putting together the dots and stumbles on Hal’s deception. 

Cahn says Turner “immediately just fit” into the Diplomat ecosystem. He shared his first scene — found in Season 2, Episode 5 — with series leads Russell and Sewell. “Those were tense scenes, and Aidan was just right at home,” Cahn says. “He just dove into the deep end and had no trouble swimming. The three of them had such a great time working together.” 

Russell adds that Turner is “a delight” to work with and thinks Kate responds to him because he’s unlike her husband in many ways. “Hal is a real force, which is what is so attractive about him,” says Russell. “And I think Callum has a very different energy and speed.” 

Poldark, the Hobbit films, Rivals

Prime Minister Trowbridge’s wife, Lydia, enters the Diplomat’s political playing field in Season 2. She’s one of the women who has sway over her husband’s chess moves. 

“Once you get to the top, the ground beneath you becomes shakier, and you realize it’s a lonely business up there,” Kinnear says of Trowbridge. “We meet his wife … and we see how the people closest to him impact his decision-making.”

But the Trowbridges’ bond is not only onscreen. Colin and Kinnear are partners in real life as well.

Penny Dreadful, Eric, Master of None

Bethan Vaughn enters the fray midway through Season 4 as a prominent figure in the UK government. Vaughn seems like a perfect counterpart for Kate, who’s excited to get to work with her. But diplomatic relations are never that straightforward. 

“On the surface, there’s a lot about Vaughn that is Kate-adjacent,” says executive producer Janice Williams. “I think Jodie Whittaker herself really brought that to the character — ‘We're just two ballsy women in a man’s world, and we’re taking it all on. We’re going to be besties.’”

Broadchurch, Doctor Who

When Kate is first introduced to Robyn Palmer in Season 4, the meeting takes a very intense turn. But will she end up being an ally to the US ambassador? 

Arcane

Frances is the house manager for the United States ambassador to the United Kingdom. She runs Winfield House, where Kate resides, and as much as she fears Kate getting into the kitchen and breaking things, she’s also developed affection for the ambassador. 

The Crown, A Gentleman in Moscow

Billie Appiah is the White House chief of staff. Tenacious and a skilled fixer, she and Stuart used to run campaigns together — so Billie often relies on Stuart’s judgment. Although she usually appears unflappable, the death of  father figure President Rayburn reveals a new side of Billie. Throughout Season 3, she has to figure out how to navigate an entirely different dynamic with President Penn, whom she previously tried to have removed from her position as VP. 

“We are in a really precarious state when we end Season 3,” says Mensah. “We learn along with Kate that she has been deceived by her own husband. It’s open season on what could possibly happen in Season 4.”

The Chair,13 Reasons Why, Bonding 

Miguel Ganon is the US secretary of state. Ambitious in his own right, Ganon disapproves when Kate goes rogue to get the job done. … And he’s not exactly thrilled with her choice of husband, either.

Station 19, Blow, Social Distance 

As the vice president’s chief-of-staff, Nora is suddenly much busier in The Diplomat Seasons 3 and 4. 

Kaleidoscope, Qabeel, Ramy

Ivy is the head of President Penn’s Secret Service detail. She is now in charge of protecting the most important American politician in the world. 

Orange Is the New Black, Younger, Ms. Marvel

In Seasons 1 and 2, President Rayburn is an aging but competent leader trying to restore America’s position on the world stage.

Better Call Saul, Grace and Frankie, Clue

Cecilia Dennison views politics as her brother Austin’s domain. When we meet the stylish firecracker midway through Season 1, she’s residing with Austin, whose devotion to his sister runs deep.

Sex Education, The Haunting of Bly Manor, The Fall of the House of Usher

The Diplomat Season 3 newcomer caught the eye of a very powerful person on the international stage. 

“Tracy is absolutely just delightful onscreen,” says Gyasi of his new costar.

By the end of the season, we learn she and Dennison are married.

The Pitt, Twilight of the Gods, Treason