October 1930. Gunshots ring out in the auditorium of a small-town cinema and when the doors are opened, a sickening crime scene greets the eyes of the horror-struck staff. The gunman has fled, leaving behind him a host of dead and dying cinemagoers and many unanswered questions. Who was the killer? What was his motive for the shooting? And just who were his intended victims?

Detective Inspector Matthew Stannard is on leave when the police are summoned, but this murder case is so big, the detective leading the investigation needs all the help he can get. When a series of mistakes leads to Matthew being put in charge of the case, he's happy to have another murder to solve, but he should be careful of what he wishes for.

Precious time has been wasted and clues, not to mention suspects, are thin on the ground. His reputation for catching killers means everyone expects him to find the gunman, but as the days pass with no arrest being made, the public grows restless and takes matters into their own hands.

The race is on. Will Matthew catch the killer first, or will the mob?