Shopping can be murder – and literally is in a gruesome case facing DS Ronnie Brooks and DS Matt Devlin, which guest-stars Rupert Graves (Sherlock).

A shop in central London becomes a scene of carnage after a frenzied attack by a man armed with a bayonet. Three people have been brutally murdered and a fourth has been left for dead. It doesn’t sound like a simple case of someone being refused a refund!

Fearing that the murderer could lash out again – and soon – Ronnie and Matt have to find him quick. They have a photofit description and are sure the killer is mentally unbalanced because of the nature of the attack. Now they just have to identify him, which they do. He’s John Smith (Rupert Graves), who’s quickly grabbed by the long arm of the law and put in front of a judge.

Senior Crown Prosecutor James Steel thinks he has a straightforward case on his hands and is a lot less ferocious than he was pursuing the killer of the teenage girl. But James has totally misread the situation. Smith is not going quietly into any dark prison and puts on quite a show in the courtroom when he defends himself. Suddenly it looks as if Smith could walk free and James has to try to convince him to admit his guilt.