Perez and his team are determined to track down the person who helped Michael Thompson's killer on Shetland. But the closer the team get to the truth in both Shetland and Glasgow, the more dangerous it becomes for all of them.
Perez struggles to deal with what has happened to Tosh as he continues to investigate the murders of Robbie Morton and Michael Thompson, but a shocking discovery finally leads him to the identity of who Thompson was going to testify against.
As the investigation reaches its final stages, Detective Inspector Perez and his team discover the person responsible for the deaths of Robbie Morton and Michael Thompson is closer to home than any of them thought.