Sisters in Arms

A run of gem robberies has the squad baffled, and the culprit turns out to be the least likely person in the story. Carol Mason is heavily pregnant and not a natural criminal. Her sister Lorraine is glamorous and manipulative, the sort of woman who always gets what she wants. Carol's first job goes wrong: a baby shop and a security guard who gets shot by accident. It's the kind of crime that doesn't look like the work of professionals, because it isn't. There's no way back from the first job; the guard's injury makes sure of that.

And the second job is a jeweller's, the one that matters. Encouraged by Lorraine, Carol walks in and the whole thing spirals. The squad closes in, and in the middle of it Carol goes into labour. The two sisters are also carrying vital evidence without knowing it, and the officers racing toward them have no idea what they're walking into.

The casting is right. Samantha Bond and Abigail Bond play the sisters: Carol's panic reads as genuine, and Lorraine's smoothness never quite hides the coldness underneath. Nicholas Ball's Hall and the usual team, Grant Masters's Matteo, Amanda Pays's Dryden, Robert Willox's Donachie, Simone Lahbib's McCarthy and Gary McDonald's Oxford, close in around them.

Tony Jordan and Roy Mitchell wrote it, Keith Washington directed, and the episode is one of the show's better uses of the ticking clock. The labour scene is handled without fuss, and whether the squad reaches the sisters before tragedy is the whole game.

It went out in November 1997, and it's the sort of story the show does best: ordinary people pushed past their limits, with the clock running and the squad one step behind. It's a long way from Lorraine's world to the inside of a jeweller's shop, and the episode walks every step of it. Carol is easier to feel sorry for than most of the show's villains, and that's the point of her.