The XXC mob is giving Scotland Yard a run for its money, but the police have no idea who they are. As the gang is London-based, Granchester's Chief Inspector Martineau is not overly concerned.
Then London gets too hot even for this gang. Cain, one of its members, decides they'll slip out of London one by one, so that Scotland Yard will think they've been done for.
Then Martineau gets a 999 call early one Sunday morning: a safe has been broken into during the night.
Martineau and team start to investigate, but they haven't got very far when there's another Granchester robbery. Martineau realises he's got the XXC gang on his hands - and that things are going to get pretty tough.