Episode 1

Line of Duty begins with a death the police would rather forget. A man is shot during a counter-terrorist operation, and DS Steve Arnott refuses to let the official story stand. The refusal costs him his posting and drops him into the anti-corruption unit, where his first target turns out to be the city's top detective, Tony Gates. Gates is the kind of officer the force holds up as an example, which makes the unit's interest in him awkward for everyone concerned, not least Gates himself.

What makes the opening work is how plainly it states the problem. Arnott keeps refusing to look away while everyone around him has learned that looking away is the safest thing. Gates, by contrast, has results and a reputation that make him hard to touch, and he knows it. The cat-and-mouse between them starts early and rarely lets up, and the show is smart enough to keep the two men mostly in the same room, trading questions and answers that never quite land. Solicitor Elizabeth Hill and Coroner Neal Foster drift through the edges of it, and Gina McKee's Jackie Laverty turns up in the credits like a promise of trouble.

Jed Mercurio wrote it, David Caffrey directed. Martin Compston gives Arnott the right mix of decency and stubbornness, and Lennie James plays Gates with a solidity that almost makes you understand why nobody wants to believe the worst of him. The rest of the room is in good hands too: Adrian Dunbar's Hastings, Darren Morfitt's Brackley, Owen Teale's Osborne, Elisa Lasowski's Wojcik and Martin Buchan's Chief Constable all get a moment to register before the case takes over.

The claim at the heart of it is simple: the most dangerous people in policing often wear the uniform. It is not a new idea, and the show doesn't pretend otherwise. But what matters is the patience with which the case is built, one interview at a time. The series will spend years testing that idea. This first episode makes it look easy.