Bäckström travels to Palma, Mallorca, with Niemi to pursue a lead in the murder of his childhood friend Sally, his only unsolved case. Meanwhile, an explosion in central Stockholm may be linked to a drug cartel.

Bäckström turns to unconventional methods to find clues and get around the Spanish police, while Niemi tries to balance the competing interests of Bäckström and Chief Prosecutor Wall.

Bäckström attempts to convince Wall and Toivonen to stay in Palma and continue his investigation, but he has his hands full with two cases that are seemingly intertwined.

When the prime suspect is murdered, Bäckström promises the man's family that he'll find the killer, before he investigates the vineyard's connection to the case.

With new evidence pointing to an unexpected suspect, a large shipment of cocaine is about to arrive in Palma. Wall seeks Morales's help to intercept the shipment before it is smuggled in to Sweden.

Bäckström puts pressure on Mellerud but doesn't get the answers he needs, while Toivonen and Niemi investigate the cartel in Stockholm. Will the truth about Sally's murder finally bring Bäckström peace?