Review: Nothing else on TV is as entertaining as this extremely stressful show

Chris Pine is still trying to hold back a sea of inkblots that are one bad hair day away from starting a nuclear war, only this time the cortisol levels and tension are even higher. Meanwhile, the Americans' fantasy nuclear missile is attacked in an operation called "Let's Bring Down Our Alliance with the British in the Swamp" (and will likely spark a third world war of words).

The Russian submarine is on the fritz and therefore remains at the bottom of the North Sea. Meanwhile, its fancy nuclear missile has been attacked by the Americans in an operation called "Let's take our alliance with the British down the quagmire" (and probably provoke a third war of words while we're at it). The prime minister, Nicole Trowbridge (Rory Kinnear), is oblivious and terrifying. At least for now, the Russians are similarly unaware of the theft, but Keith Wyler (Kerry Russell), the US ambassador to Britain, predicts that the eventual discovery will blow the Kremlin's Oshankas sky high. "Russia will come to get its underling," she warns her unblinking husband—and current US Vice President—Hall (Rufus Sewell). When they realize their doomsday weapon is gone, they'll lose their stuff and attack Britain! "Hmm," replies Hal, one of whom he suspects has more mobile fish to fry. "Mmm."

This is where we find ourselves as The Diplomat returns for a fourth series of highly innovative geopolitical diversions. That should be said; We're teetering on the precipice of the Great War, a situation almost entirely attributable to the whims of the President of the United States, Grace Penn (Allison Janney). Yes, but also, in a very real sense, woohoo. Because there are few things as entertaining as a bad-tempered "Diplomat," even if the stress of doomsday shows requires a lot of diaphragmatic breathing and the odd diplomatic dash to the toilet.

Transatlantic thriller Deborah Kahn has long been fascinated by the real-world ramifications of her politicians' high-rollers, every twist and turn infused with the suspicion that humanity is one bad day away from Armageddon.

This time, the stakes and cortisol levels are even higher, and Kate once again finds herself desperately trying to avert political and personal catastrophe.

So it's on to Windsor Castle, where we see the Penns and the Wailers diverted to the (currently King-less) royal estate after a group of protesters stormed the M25.

Keith asks Hal to tell the President to tell the Prime Minister that the Americans have taken the Russians' weapons. This, apparently, "burned the damn mess". Hal, naturally, doesn't want to do this. "I do not accept your confession," he said sullenly. "That's stupid." He's also unimpressed by his wife's comments that he and his boss "look shady together."

"You're jealous," he smirks. And he is disappointing. Not only because of his wife's close relationship with Grace, but also because of the fact that Hal's job allows him to go around doing worldly smart things while his job keeps him stuck in rainy London pretending to enjoy the Garibaldis of Trowbridge. Kate is also jealous of Grace, and Grace's husband, Todd (Bradley Whitford), and Calum Ellis (Aidan Turner), a spy with throbbing thighs. She would probably have been jealous of the royal corgis, too, if they hadn't all been removed from Windsor before the Americans arrived (a wise move: Grace mistook them for sheep and tried to serve them "on rye").

Several big things happen, including snipers, security breaches, and globular Russians tucking their chins into their chests while muttering about the fall of the West. Tension! Almost cartoon nonsense! But, as always, it's the little things that are most fascinating: the ever-present small shifts in power. Streaks of love in the never-ending 4D chess game that is the Wailers' marriage.

The cast is fantastic as always. At least Whitford as Penn and Sewell as dispassionate Hal, the latter's performance a series of fleeting tics behind the cheeks that could have cobwebbed off the browbone.

But hess, here comes Kate with another semi-flirtatious rant at her husband's affair with the President. "I mean," he spills. "This is dangerous. The two of you together, falling into the abyss…