The hunt is on for Malone's attacker, Malone seems to know who is responsible, but isn't keen to share the information. Perez and Rhona believe Andreas Hagan, the health and safety officer at Forst Energy is responsible for covering up corporate manslaughter and is their strongest lead in Sally McColl's murder. Meanwhile, DNA testing in the Kilmuir case yields a surprising result.
Thomas Malone returns to Shetland after serving 23 years in jail for the murder of teenager Lizzie Kilmuir, a crime he swears he didn't commit. Whilst most of the islanders are convinced of Malone's guilt, the appeal and his subsequent release have thrown up the possibility that someone else could be responsible for Lizzie's murder.