Atonement

Billy McCree is found dead in his workshop with his severed hand lying beside him. It's a message as much as a murder, the kind of flourish that tells the police who they're dealing with before forensics has anything to say. Everyone in the team knows who it's meant for. Jim Naysmith is out of prison after a twenty-year stretch, and Billy's evidence is what put him there. Naysmith is the obvious suspect before the investigation even starts.

Burke and Reid work another member of Naysmith's gang, chasing the old network that still orbits him. Ross, meanwhile, is flattered when Mary Cullen, a young law student, asks to shadow him. Gemma Kerr isn't flattered at all. She sees something in Mary's sudden interest in Robbie that the DI himself is too pleased to notice, and the episode lets that doubt sit there without forcing it. The suspicion around Mary never hardens into proof, and the show is content to leave the question hanging.

Julie Dixon and Glenn Chandler wrote it, with Morag Fullarton directing. Blythe Duff's Jackie Reid, Alex Norton's Burke, John Michie's Robbie Ross and Colin McCredie's Stuart Fraser anchor the case, Lesley Harcourt's Gemma Kerr watching from the sidelines. William Macbain plays Jim Naysmith, Frances Thorburn is Mary Cullen, and the McCree family circle is rounded out by Iain Robertson as Ryan McCree, Linda Duncan McLaughlin as Morag McCree and Alex Harvey as Neil Mosby.

The severed hand is the kind of detail the show does well: grotesque and specific, its meaning impossible to misread. The revenge plot is simple; the suspicion around Mary is messier, and that's where the episode's real interest lies. Atonement is the title, and it does double duty: the dead man paid for his evidence with his life, and the living are still working out what they owe. It's an enquiry that keeps asking whether twenty years in prison settles a debt or just postpones it.