Mistaken Identity (1)

Denton is bracing for the arrival of Babcock from Her Majesty's Inspectorate of Constabulary, the inspection that will decide the station's funding, and Mullett is in a state of controlled panic. Frost, as ever, is a liability — old-fashioned, unapologetic, and about to be handed a new detective constable, Ronnie Lonnegan, a young West Indian woman whom he manages to offend within minutes with a string of ill-judged remarks. It is the season opener's way of announcing its themes: inspection, prejudice, and a serial killer working the edges of all of it.

The case is the worst sort. An unidentified body is found in a reservoir, and a couple — Jean and Paul Harris — are found bound and burned alive in their own home. The prime suspect is the Harrises' handyman, Mike Patterson, who was sleeping with Jean; the runner-up is Paul's father Arnold, who loathed her. Forensics link the two crimes — garden lime at both scenes — and Frost, reluctantly, brings in psychologist Pam Hartley, who tells him he is hunting a true psychopath, someone who enjoyed watching the Harrises burn.

Around the main case, the episode spins a smaller, sourer carousel: a turf war over ice cream vans in which one company is dealing ecstasy alongside the 99s, and the disappearance of Melanie Monkton, a young woman whose beloved horse was euthanised after a mysterious break-in. Frost, coping with a dog whose homeless owner was beaten, moves between the threads with his usual grumbling competence, while the HMIC inspector watches him the way a hawk watches a field mouse.

Mistaken Identity (1), written by David Gilman and directed by Roger Bamford, is the series' most explicitly institutional episode in years — an inspection hanging over every scene, and a detective whose methods are on trial as much as the killer's crimes. Susan Penhaligon's Pam Hartley, brisk and unflappable, is the first profiler who genuinely holds her own against Frost, and the episode sets up a two-part puzzle that will end with the inspector's verdict — and Frost's.

An institutional drama disguised as a serial-killer hunt, with an HMIC inspection hanging over every scene — and Susan Penhaligon's profiler giving Frost real competition for the first time. An institutional drama disguised as a manhunt.