Wren Boys (1)

Series six opens with a body from the show's back catalogue of horrors: Davy, a teenage boy found on a building site some years ago, drowned in wet concrete. Suicide, accident or murder? The team has to work out which, and the case promptly grows legs. A fragment of human ear turns up in the boy's stomach, and that one grim detail ties him to another teenager who was dumped, badly injured, at a hospital around the same time. Two cases become one.

The ground itself complicates things. Where the body was found belongs to a Catholic abbey that's about to be dissolved, and the abbey owns a shrine which might hold evidence and therefore has to be taken apart. That job lands on DC Stella Goodman, who wants it about as much as you'd expect. There's a quiet cruelty in handing your most junior officer a crowbar and pointing her at someone else's sacred objects, and the episode doesn't pretend otherwise.

Trevor Eve is DSI Peter Boyd as ever, with Sue Johnston's Dr Grace Foley and Wil Johnson's DI Spencer Jordan alongside him. Félicité Du Jeu is Stella Goodman, and Carey Mulligan plays Sister Brigid, with Edward MacLiam as Joe McDonagh, Ruairi Conaghan as Sean Killigan Jnr, Tony Scannell as Papa McDonagh and Daragh O'Malley as Sean Killigan Snr filling out the community around the abbey. The significant new arrival, though, is Tara Fitzgerald as forensic scientist Dr Eve Lockhart, who makes an immediate impression on the case and, in time, rather more than that.

Tim Fywell directs, from a script by Declan Croghan and Barbara Machin.

The abbey setting could have been decorative. Instead it gives the investigation real friction: police access versus religious property, old loyalties versus old sins, all of it sitting on top of a boy nobody came forward about. Part one does its job properly. It asks its terrible question, hands Stella a task she'll hate, and leaves the answer buried in concrete for another forty-odd minutes.