Annika Strandhed is the Detective Inspector heading up the newly-formed, Glasgow-based, Marine Homicide Unit (MHU). The relationship between Annika and Morgan, her teenage daughter, is the basis for a sub-plot across all the episodes. Annika regularly breaks the fourth wall to communicate directly with the audience about aspects of the current case and personal reflections. She is of Norwegian ancestry, and often refers to Norwegian culture and folklore.

In the last episode of Series 1, Annika reveals to the audience that Michael McAndrews is Morgan's biological father.

In Series 2, when Blair announces her pregnancy and Tyrone reveals he will be leaving, Annika puts off telling Michael. Soon after meeting DC Harper Weston (Varada Sethu), she finally tells Michael.

After Tyrone leaves, Harper becomes a part of the team. As the series progresses, Annika and Michael have to work out how and when they are going to tell Morgan about her father, but after Erin dumps her, they decide to wait. In the series Annika rekindles her relationship with Jake; however, Annika's father arrives and as she begins to build a few bridges with him, Morgan suddenly asks if Michael is her dad.