This post contains spoilers from The Diplomat season 3 episode 1 from this point forward.
The Diplomat season 3 sure opened with a bang as President Penn took office and quickly shook things up for the Wylers. Even though Hal had been steadily campaigning for Kate to score the vice presidency, Penn shocked them both by asking Hal to be her vice president. Once they're alone back home, Hal insists that he still wants Kate to have the job, and she will one way or another.
Kate appears to be sorting through complicated feelings, but we know that above anything else, she is rational. She tells Hal to accept Penn's offer. She goes for a walk with her security to a bar, and that leads to a flashback to Baghdad in 2010. Kate argues her position to Hal after arguing with a colleague, and Hal accepts her position. There's more to this story, though.
While talking to Nora about vetting vetted for the vice presidency, Hal sticks his neck out for Kate to have a position and job beyond Second Lady. Even after Kate talks him down, Hal continues to broker with Nora. As Kate packs up her office and prepares to leave her post as ambassador, Eidra arrives with the news the Roylin has died. Eidra fears that she will be fired over this death.
Hale fights for a special envoy position for Kate
Because she's leaving London with Hal, Kate can't help Eidra through this Roylin situation. During his meeting with Billie, Hal continues to push for Kate to have a position in the administration. He gets Billie to agree to a special envoy to Europe, which he reveals to Kate with a paper on a window. When he explains the job terms to Kate, she's ecstatic about what she will get to do along with Second Lady.
Stuart informs Kate that he intends to resign when she leaves, but she has suggested that he becomes an ambassador. She also breaks the news that she will be appointed to special envoy to Europe, and she asks him to come with her. But she doesn't know about funding or the limits of the job, which is enough of a lack of information for Stuart to turn down the job.
Kate takes a meeting with Trowbridge and Dennison to share the update on Roylin's death, which takes some heat off Eidra. Trowbridge blames Kate, but he doesn't want her to be fired over it (though she can't reveal why she's really leaving London). In fact, it's unclear what he wants. When it's just her and Dennison, she breaks down in tears and teases what's next for her.
How Hal proposed marriage and Kate's shocking decision
In the flashback to 2010, Hal reveals to Kate that he won't be returning to Baghdad, and she demands to go with him. It's quite the change to see Kate fighting for Hal. Back in real time, Kate and Hal take a meeting with Stuart and Nora about the photos of the couple from the plane. However, Stuart proposes Kate staying in London as ambassador. Kate seems to be considering this.
After that conversation, Hal kind of crashes out and asks Kate if she wants a divorce. She doesn't want a divorce, she doesn't want to stay in London, she's going with him, and she wants to leave it at that. The flashback returns and shows the moment that Hal proposed to Kate. It wasn't romantic. It was very "them." In the middle of tense situation and very casual. He fabricates an engagement ring out of a twisty tie and they kiss in the back room of the restaurant they were in.
Having seen that pivotal part of their backstory, Kate and Hal's hectic dynamic makes all the more sense. Kate says her goodbyes and leaves with Hal. She looks back at Winfield longingly before they drive off. On the tarmac, Kate gives Stuart a hug, but they only exchange knowing grins. As she watches Hal board the plane, she remains beside Stuart. Without a word, Kate makes her choice to stay in London.