"When human remains are found in the stomach of a dead wolf in the remote northern town of Haparanda, Sweden, policewoman Hannah Wester knows that this summer won't be like any other. The remains are linked to a bloody drug deal across the border in Finland. But how did the victim end up in the woods outside of Haparanda? And where have the drugs and money gone? When the secretive and deadly Katja arrives, unexpected and brutal events start to pile...

When a prominent French politician is found dead on the border between the UK and France, detectives Karl Roebuck and Elise Wassermann are sent to investigate on behalf of their respective countries. The case takes a surreal turn when a shocking discovery is made at the crime scene, forcing the French and British police into an uneasy partnership.

Unable to locate Matthew, Marcella begins another line of inquiry, looking more closely at Grace's brother, Henry. Jason's suspicions are also aroused, and he decides to confront Henry at his home.

More than a decade after quitting the force to start a family, former detective sergeant Marcella Backland is devastated by the breakdown of her marriage. When a detective comes seeking her opinion on an unsolved case she had investigated, Marcella returns to police work to try to catch the killer.

The Gibson family contacts the police about Grace's disappearance, while Marcella tries to make sense of her vague memories of visiting Grace the night before. Sex-worker Cara's habit of robbing her clients lands her in danger.

Marcella interviews Peter Cullen in hopes of closing the case on the 2005 murders. Jason gets his job back at DTG Construction, but he struggles to move past Grace's death.