When body parts belonging to a young Nigerian man are discovered on the island, Perez and the team investigate. They use CCTV to trace the victim's last movements, and after scrutinising his emails and social media accounts, the case takes a sinister turn.

Carla and Prentice Hayes are found murdered in a violent knife attack. Jamie Hayes is missing, initially leading the team to speculate that he could be responsible. But Jimmy is convinced that Jamie could not have mutilated his mother in this way. Aware of her altercation with Prentice the previous evening, Perez pays a visit to Olivia Lennox. She's in her room, shaken, with blood on her clothes. Could she be responsible or an innocent bystander?

Calum is rushed to the hospital after attempting suicide while in custody, which brings Sandy under internal investigation for providing him with a pen. Jimmy travels to Glasgow to investigate human trafficking, but has he brought his family into danger? Meaning, Zezi sees a way to escape from her captor.

Convinced that Zezi is being held on Shetland, Perez and the team ramp up the pressure on their remaining leads. Personally, Perez finds himself in turmoil after his kiss with Alice.

The discovery of Niki's body intensifies the search for Zezi. Perez feels that time is running out. A desperate Olivia tries to get information from Jamie Hayes.

With Olivia giving up hope, Perez at last closes in on Zezi's location. But can he reach her before it's too late? Duncan is traumatised after his discovery on the beach.