Hammer

A run of violent robberies on Maggie's patch, all bearing the same pattern and all carried out by women. The squad has to decide whether they're hunting a gang or one very busy woman with a wardrobe of disguises. The robberies come with violence attached, which raises the stakes; whoever is behind the disguises is not playing. Either answer is a problem, because nobody on the team is used to looking for female robbers. But the episode enjoys watching them adjust.

Lesley Manville's Shirley Davis and Leslie Ash's Maureen are the two most visible suspects, and the show is smart enough to let them be people rather than walking alibis. Rosalind Ayres's Frances West comes at the case from a different angle altogether. The disguises are the episode's best idea, one woman becoming several before the squad's eyes. The pleasure here is procedural: wigs, hats, testimony that doesn't match, and a pattern that keeps shifting just as the squad thinks it has the measure of it. The squad's frustration is part of the fun: witnesses who change their story, and the growing suspicion that the answer is simpler than it looks.

Tony Parker and Terence Feely wrote the script, Tony Wharmby directed, and the whole thing runs on the reliable engine of the regular squad: William Marlowe's Russell, Derek Thompson's Fenton, Brian Gwaspari's Croft and Paul Moriarty's Barratt all get their turns. Derek Martin's Nellie Jackson is among the faces the inquiry turns over, with Mary Maddox's Rosalie on the edges.

The title gives the game away about the weapon, and the episode is content to let the hammer do its work in the background while the identity question drives the hour. It's a neat puzzle piece, the sort of episode that reminds you how much mileage the series gets out of a single good idea, worked steadily and without fuss.