Last Year's Model

Barnaby has begun to doubt the evidence that helped convict a murderess, and that doubt is the whole engine of this episode. It is a strange pleasure to watch the DCI turn over a case he has already won, poking at details he once accepted without a second thought. The more he looks, the less watertight the evidence appears, and the more he worries about the verdict he helped secure. But outside the courtroom the details keep shifting, and the episode keeps coming back to a question the show usually leaves alone: whether a verdict built on shaky evidence deserves to stand.

The story follows him as he re-examines the case, going back over old ground and finding that the certainties of the original trial have begun to fray. And every visit to the old witnesses brings a fresh version of events, which is exactly what unsettles him. DS Ben Jones works alongside him, Joyce and Cully provide the usual domestic calm, and Dr George Bullard turns up with his professional eye. Around the edges of the investigation move Annie Woodrow and Lance Woodrow, played by Saskia Wickham and Miles Anderson, along with Felicity, played by Helen Dallimore, and John and Ed Trevelyan, in the hands of Brian Protheroe and Emily Gloyens.

David Hoskins and Caroline Graham wrote it, with Richard Holthouse directing. The story moves at its own pace, which suits a detective who is second-guessing his own past. The cast carries the uncertainty well, and Nettles gets to play a Barnaby who is quietly, professionally rattled rather than merely busy.

What stays with you is the flicker of doubt that follows any big arrest. This is a murder mystery less concerned with whodunnit than with how sure anyone really was, and for viewers who like their detectives to think, that is a welcome change of pace. It is not the show's most dramatic episode, but it may be one of its most thoughtful.