Five years after Duncan Percival is left in a vegetative state following a vicious attack, he finally dies. The case has now become a murder investigation, and DCI Hennessey and DS Yellich are brought in to renew the evidence and re-interview the suspects. As they delve deeper, bodies start turning up, and the detectives are drawn into York's criminal underworld where grasses are punished and the gruesome Chelsea Smile is the favoured method of retribution . . .