When a young man disappears on a ferry crossing and a small boy ends up in intensive care, DI Jimmy Perez and his team become convinced the two events are connected.
On the ferry journey from Aberdeen to Shetland a passenger, Leanne, witnesses an altercation between two men. She starts talking to one of them, Robbie, but discovers the next morning discovers that he has vanished from the ferry overnight.
Later that day a little boy ends up in intensive care, after eating pills he mistook for sweets found on the beach. DI Jimmy Perez searches the shoreline and recovers a rucksack – but not before a hooded figure tries, but fails, to snatch it. Back at the station, Perez, Tosh and Sandy discover that the bag contains a stash of pills and the remains of a ferry boarding pass.
Later, Leanne recognises the distinctive silver rings she saw the ferry attacker wearing. This leads Perez to track down jewellery designer, Freya, who reveals she gave the rings to her friend, Michael. Perez questions a hostile Michael and is unconvinced by his version of events. However, his investigation is quickly thwarted when Procurator Fiscal Rhona Kelly reveals Maguire has lodged a formal complaint against Perez.
Now a missing persons and drugs case, Perez’s investigation gathers pace after a body is discovered in grisly circumstances. With suspicions roused, Perez and his team delve deeper, stirring up far-reaching consequences for them and the local community.