Bloodsport

Noel Cash, a young boxer, is found battered and dumped by the motorway. His father Eddie, who doesn't yet know his son is dead, comes to the police with a different complaint: the lads from his boxing gym are being lured into cage fighting by Don McGreevy, a shifty operator whose fight club sits at the centre of a murky economy of gambling and lap dancing. It turns out Noel boxed there to get out of debt. And it turns out Robbie Ross is a regular visitor to the same club, which lands close to home when his own gambling addiction comes out in the open.

Texts on Noel's phone point to Anita Holland, a pole dancer who worked at McGreevy's club, and to her boyfriend Bomber Dunne, a pimp who was jealous of her friendship with Noel. The jealousy angle is easy to dismiss until Bomber's name keeps coming up, and the episode lets it breathe. But before the team can close on anyone, Eddie Cash is murdered too. Burke leans on McGreevy's right-hand man, ex-boxer Alamo Higgins, and presses him until the killer's name comes out.

Glenn Chandler, Declan Croghan and David Kane wrote it, Douglas Mackinnon directed. Alan Tall is Eddie Cash, Philip Whitchurch is Alamo Higgins, Monika Miles is Anita Holland, David McKay is Cosmo Lennox, Kristian Hart is Bomber Dunne, Moyo Akandé is Kerrie Macdonald and Davood Ghadami is Duncan Clark. Blythe Duff, John Michie, Alex Norton and Colin McCredie work the case.

The episode deals out its violence in rounds, and Robbie's secret gives it an extra sting: the detective who should be pulling people out of this world is paying to stand inside it. The fight club crowd is drawn with relish. Robbie's entanglement means the case follows him home, which is where this show always liked its trouble to land. It's a grim world, and the episode doesn't look away from it.