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

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.

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.

Calder and Tosh discover the truth behind Rossi’s mission. They must identify Annie’s killer before he can exact his revenge.

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