BBC drama SS-GB delivers a brilliantly unsettling alternative history of the Second World War

In this alternative history thriller, it is 1941 and the country is under the yoke of German occupation, having lost the Second World War at the Battle of Britain. Our protagonist is talented young Douglas Archer (Sam Riley), a Scotland Yard detective forced to negotiate life under his new German bosses. Also starring are Kate Bosworth as a mysterious American reporter, Maeve Dermody as rebellious secretary Sylvia, and James Cosmo as old-timer Sergeant Harry Woods.

In SS-GB, people are making do in this grey and defeated city. An egg or a cup with a spoonful of "real tea" is a luxury. Jumpers are unravelled for wool, while the Germans round up the prostitutes and keep the Brits on edge. Director Philipp Kadelbach has succeeded at keeping viewers on edge, too, shooting the drama through with a feeling of deep unease.

But though everything seems to be lost, the Resistance fights on.

The story opens during German-Soviet friendship week, but as a Spitfire is flown in to be presented during the ceremony (to the victors, the spoils), a Resistance fighter bursts out into the open and shoots the Luftwaffe officer.

At the same time, an antique dealer is found shot to death in suspicious circumstances.

It is a brutal start to an episode which otherwise seethes with just the warning of violence to come. The organised brutality of the occupying power bubbles underneath, but comes out when an SS officer reminds Sam and Harry to do their jobs or face a firing squad, or when the genealogy investigations begin and the box of yellow "Jew" patches arrive at Scotland Yard. Just the sight of that box full of Stars of David is enough to put the dread in the pit of your stomach.

The TV adaptation is the work of James Bond screenwriters Neal Purvis and Robert Wade, and they sure know how to write a villain – so they have done an excellent job with the thoroughly dislikable SS colonel Huth (Lars Eidinger), who has been despatched by Herr Himmler himself to oversee the investigation into the death of the antique dealer. As Archer has already clocked, there is more to the case than first meets the eye.

Huth's arrival puts forces the issue: what are Archer's political allegiances?

It's an issue driven home by the blunt questions of his son and his landlady's kid: does he work for the Gestapo, like their school-friends say? Is that why he gets a nice car? And the question he has to ask himself: can the Met really continue business as usual when policing is political?

He swerves the children's enquiries with the lame excuse "the Gestapo are in the building next door" and delivers a pep talk about how things will go back to normal once all of this is over, but of course he knows things aren't so cut and dried. Archer is in an awkward, morally compromised position. And working with the Nazis puts him in danger of assassination by the Resistance, but what the occupying power is doing to his country clearly causes him revulsion.

There is a lot of material from the novel to pack into five one-hour episodes, but nothing feels rushed. Refreshingly, the drama is also intelligent and nuanced (my one complaint is that it is slightly mumbly in places, making your brain work even harder than it already has to).

SS-GB refuses to spell things out or simplify moral dilemmas. But at the heart is one simple question: in Archer's place, what would you do?

SS-GB airs from Sunday 19th February at 9pm on BBC1