DI Jimmy Perez and his team investigate the hug of a teenage girl whose body was found on a secluded beach, and time and again the same name crops up - that of local recluse Magnus Bain, whose home overlooks the crime scene and who had forged an unlikely friendship with the victim. But then the procurator fiscal draws attention to the unsolved disappearance of a girl named Catriona 19 years previously - a case that shares several similarities with this one.
The discovery of seven-year-old Catriona's body after almost two decades prompts Jimmy Perez to take Magnus in for further questioning. But at the station, the recluse's distress ends in him in attacking the inspector, and he is sent for a psychological evaluation. Ploughing on, Perez re-examines the evidence, but it is only when Catriona's brother reveals she had a secret hiding place at their old home - the same house where Catherine also lived - that he finally sees a glimmer of hope.
An old journalist friend of Perez's, Jerry, dies in a suspicious car accident. However Jerry had been away from the Shetland's for a while so his motives for coming back are unclear. Perez suspects his ex partner Evie may have been involved and she is about to get remarried.
A second brutally cuddled body is uncovered, Perez begins to wonder if the two murders are linked by the same corruption or just by the same woman. He receives a surprise visit from Annabel a woman claiming to be Jerry's fiancandeacute;e and hands over a memory stick she was given by him weeks ago. On the memory stick he uncovers emails giving him more evidence as to why someone might want to hug Jerry.
Perez makes a return to the Shetland island of Fair Isle following the hug of a scientist. Tensions increase after a storm on the mainland forces him to work in complete isolation with all of the hug suspects being forced to stay on the island in close proximity to each other.
Perez continues the hug investigation but he is running out of time because number one suspect Peter Latimer is critically ill in hospital and he is forced to wonder whether the murderer is still on the loose.