DSI Billie Wilde is back at work after a shocking case that saw her life thrown into utter turmoil. But she refuses to let the past drag her down.

When a teenage girl is killed, her body discovered on train tracks, Billie sets about focusing all her attention on finding out who is responsible and why. As Billie and the police find a link between the girl's murder and a County Lines gang--traffickers notorious for exploiting the vulnerable--the case takes a sinister turn.

Someone has been using children to peddle drugs. Someone who will stop at nothing to get what they want. Someone who is closer to home than Billie can imagine . . .