When a young man disappears on the Aberdeen to Shetland ferry crossing and a small boy ends up in intensive care, DI Jimmy Perez and his team investigate, becoming convinced the two events are connected.

DI Jimmy Perez is convinced that Michael Maguire is somehow implicated in the death of Robbie Morton. But with the investigation seemingly under threat before it's even started, he faces an uphill battle to uncover the truth behind Maguire's silence.

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.