Whilst on the ferry from Aberdeen to Shetland a passenger called Leanne sees an altercation between two men. She begins talking to one of them who is called Robbie, but the next morning she finds out that he has vanished from the ferry during the night.
Perez believes that Michael Maguire is implicated in the death of a young man, found in a shipping container. With the investigation under threat before it's even began, Perez and his team have to deal with an uphill battle to find out the truth behind Maguire's silence. Perez, Tosh and Sandy soon work out that Robbie's body was retrieved from inside a shipping container and as it can only be locked externally, they now look for a murderer with Maguire as their number one suspect.
Perez and Tosh's investigation takes them to Glasgow, where they attempt to uncover the truth regarding Maguire's death and his connection to Robbie Morton.
The hug investigation continues and Perez and his team are determined to find out the identity of the person who helped Michael Thompson's hugger. Perez, Sandy and Tosh are soon all under threat.
Perez finds it hard to deal with what has happened to Tosh as he continues to take a look into the murders of Robbie Morton and Michael Thompson.
Perez and the team discover that the person that they believed to be responsible for the murders is closer to home than any of them thought. A new light is shone on the hug of Michael, when the team discover who assaulted Kelly. Leanne is struggling to deal with the emotional aftermath, after been shot.
Perez is troubled when he discovers that Michael's witness protection handler Asha was in Lerwick on the same day that the email was sent out. The team dig deeper into Asha's past and discover a connection to one of McCall's team.