The Diplomat season 4 ending: Kate is out, the Russia crisis isn't

Season 4 of Debora Cahn's political thriller arrived on Netflix on October 15, all eight episodes at once. Keri Russell plays Kate, the American ambassador to the United Kingdom. Rufus Sewell plays her husband Hal, now vice president, and Allison Janney plays President Grace Penn. The finale is called "Warships."

How the crisis started

It goes back to the end of season 3. A Russian submarine carrying the Poseidon, a nuclear-powered torpedo, went down several miles off the northeast coast of England. Kate argued that the U.S. and Britain should bury it in cement. Grace and Hal secretly sent an American submarine to take it instead, and the public story became that the weapon had been sealed in concrete.

Season 4 makes that secret impossible to keep. Prime Minister Nicol Trowbridge resigns midseason, and his replacement, Jodie Whittaker's Bethan Vaughn, knows the Americans took the Poseidon. When Russia asks permission to recover the bodies of its sailors from the wreck, Vaughn says yes. Once the Russians reach the submarine, they'll see the weapon is gone.

How Grace escalates

Grace's answer is force, and each step costs Kate something:

• She orders Kate to make Vaughn withdraw the permission, or, in Grace's words, "I'll send warships to do it for her."
• Kate softens the message when she delivers it. Grace finds out, and the two clash over dinner on an Italian terrace.
• Grace sends her husband Todd to London as a "special envoy." He suggests the U.S. could harm any British citizen who gets between American warships and the Russian submarine.
• Stuart Heyford, Kate's deputy, files a formal dissent cable against the warship plan. Grace has him recalled to Washington.

Then comes the G7 summit in Florence. Grace takes the floor before Vaughn can expose her, admits the U.S. has the Poseidon, and says American forces will fire on any country that interferes, allies included. Her goal, she says, is "keeping Russian warships and surveillance vessels and tactical weaponry out of the European seas."

Kate is out

Kate kisses Hal, tells him she loves him, takes off her lanyard and resigns in front of the room. Chief of staff Billie Appiah and Miguel Ganon walk out after her. Then Hal steps out of the shadows and joins them.

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As Cahn told TV Guide, "I don't think she was planning to march out and talk to the press." But outside, Kate turns to the cameras and announces that the vice president would like to make a statement. The screen goes black before he says a word.

"I think he chooses right versus wrong as he understands it," Cahn told TV Guide of Hal.

The crisis isn't

When the season stops, this is where things stand:

• American warships are headed for Britain's coast, under a public order to fire on anyone who interferes.
• Russia still has British permission to go to the wreck, and the season never shows its response.
• The Poseidon is in American hands, at a location the show never reveals.
• The cover story that it was buried in concrete is now gone, admitted by the president in front of the G7.
• The vice president is about to make a statement, and nobody has heard it.

Netflix hasn't announced a fifth season. Asked where it would pick up, Cahn answered: "That's a really good question. Stay tuned, my friend."

Previously we wrote: What happened to River Cartwright? Slow Horses' only hint is a Lamb joke about the afterlife