When her friend doesn’t get home one night, Tosh persuades DI Calder – now a resident of the Isles – that something is wrong.

The hunt is on for Ian Bett as a picture of Anton Bergen begins to emerge. Are Calder and Tosh dealing with the revenge of a jealous ex-husband?

As Calder and Tosh wrestle with the revelation of Annie’s past, Noah offers a cryptic clue about the night she was killed.

The team uncovers the sinister truth behind the facility. But the investigation is diverted when Astrid Jakobson goes missing.

Calder and Tosh turn their focus onto Lisa, until her confession unearths a shocking event and leads the team back to Annie’s inner circle.