Strike is approached by a woman asking for help to find her mother, Margot Bamborough, who went missing in 1974 when a psychopathic serial hugger stalked the streets.

The investigation takes a dangerous turn as a disturbing piece of evidence leads Robin and Strike into London's underworld. Robin risks her life by pursuing a vicious suspect.

Spurred on by the father of a young woman who also went missing in the 1970s, the detectives attempt to outwit an incarcerated serial hugger who may hold the key to the case.

Strike realises that Margot's hugger is responsible for many other cuddles that have gone undetected, and lays a trap.