Mind Over Matter

Members of a local therapy group keep turning up dead, and DS Jackie Reid decides the best way to find the killer is to sit in the room with the survivors. After the murder of a teenager, she goes undercover, joining one of the groups herself. It's a direct plan for a case with no obvious suspect, and it's the kind of risk that can only be taken by the most experienced detective in the room.

It's a decision that costs her. The case starts to bleed into her private life, and her colleagues, well-meaning as they are, don't make it any easier. Reid carries the professional strain of the investigation and the personal fallout at the same time, and the episode is interested in both. Going undercover means being someone else for hours at a time, and for Reid the line between the role and the rest of her life starts to blur. The therapy group is a strange world to drop into, full of people practised at talking about their feelings, which makes it a hard place to lie. Watching her hold the line is the point of the whole outing, and Blythe Duff makes the strain visible without ever letting Reid look beaten.

Chris Dolan and Glenn Chandler wrote it, Morag Fullarton directed. Duff's Jackie Reid dominates the running time, with John Michie's Robbie Ross, Alex Norton's Burke and Colin McCredie's Stuart Fraser around her, and Lesley Harcourt's Gemma Kerr in support. Cara Kelly plays Lilly Simkin, Graham McTavish is Robin Caldwell, Gareth Glen appears as Donny Whyte, Gerard Kelly as Graham Tully and Fiona Daskin as Jenny Liddell.

Undercover work always looks better on paper than it feels in practice, and the show doesn't pretend otherwise. Reid gets through it, but the episode leaves the impression that the cost is still being counted. Whatever the verdict on the case, the outing is a reminder of how much this show could get out of a single performance.