Shetland

DI Ruth Calder is talking to Malcolm Kidd, a jittery young man holding a shotgun. His brother's dead body lies on the floor between them. Tosh and the rest of the cavalry are waiting outside. It has to end at some point, but how?

Later that night, Tosh attends her friend's birthday party and witnesses the argument of two married friends, Annie and Ian Bett. Their nine-year-old son, Noah, tells Tosh his parents are separating. Before they leave, Annie arranges a meeting with Tosh the next morning – she wants to speak to her about something important. Annie and Noah are staying with John Harris, a mussel farmer, and his sons Patrick and Fergus. But when Tosh arrives the next morning, there's no sign of Annie's car, and she's not picking up her phone. Where are Annie and Noah?

A picture of victim Anton Bergen begins to emerge, leading Calder and Tosh to question whether they're dealing with a revenge killing. Furthermore, strange details begin to suggest there's a hidden side to Annie Bett. They attempt to fill in the pieces by speaking to Bergen's employers Karin and Stefan Jakobson – a wealthy Swedish couple who arrived in Shetland six months ago - and discover Bergen was a nurse to their chronically ill daughter, Astrid.

Elsewhere, a hungover Ian is found slumped in an abandoned building, wearing bloodstained clothes. Unable to answer police questions, Ian is released. That is, until messages on Ian's phone shock Tosh to the core.

Meanwhile, at the mortuary, Cora reveals a shocking discovery from her post mortem.

Rossi reveals details of Annie's hidden history, leaving Tosh and Calder to wonder whether they might be dealing with something bigger and more dangerous than previously thought. Noah gives a heart-breaking account of the fateful night but falls short of identifying the killer. He does, however, give Calder a strange, cryptic detail which spikes her interest.

As conspiracy theorist Angus Wallace monitors the marine research facility, the opportunity to infiltrate presents itself. When he fails to return, his friend Lisa raises her concerns to Rev Alan Calder.

Meanwhile, an emotional John Harris opens up to Tosh about his fondness for Annie. However, when a new connection to Bergen is unearthed, the team quickly grow suspicious of John's sons, Patrick and Fergus. As the Harrises find themselves under the police spotlight – and John wrestles the loss of his friend Annie - their family dynamic begins to unravel with shocking consequences.