The police never found the killer, and the case remains unsolved. When Fielding's desperate parents ask Forensic Psychologist Jo McCready to help find their son's murderer, she discovers a piece of evidence that changes everything. As she investigates, Jo gets a call from DCI Callum Ferguson about an alarming development.

At a busy train station, a man has randomly and viciously attacked another passenger before fleeing the crime scene. But Jo is convinced this is no random attack. She believes the two crimes are tangled up in the same web of deadly local secrets.