Shetland

Calder decides to stay on and investigate the previous night's discovery. Tosh welcomes her support as the revelation of a tattoo sends the case in a sinister new direction.

When a mysterious tribute is left at the crime scene, Tosh and Calder are drawn to the house of Tom Knox, a nervous and reclusive figure whose family have a longstanding feud with the Bains. Tom is guarded about his relationship with Ellen and the detectives grow suspicious.

Elsewhere, Sandy visits a mental health facility where Ellen stayed briefly before moving to London. He discovers that she was admitted by her cousin Heather and looked after by Dr Azir Sadat. Both blame Ellen's breakdown on her hard partying lifestyle but it becomes clear that there are hidden layers to Heather and Azir's relationship.

Tosh receives a shocking call from Cora at the mortuary with a horrifying development, while Calder's past and present collide when she hears a startling revelation about her father.

As Calder and Tosh race to prevent disaster, they are drawn to a horrifying fire on a remote hillside and a brand new prime suspect in this increasingly complex and unnerving case.

In the interview room, the new prime suspect talks about his special connection to Ellen Quinn. He claims that his funeral rites were an act of love, part of an ancient religion. But Tosh and Calder see an attempt to destroy evidence.

While Grace berates Calder and Tosh over their handling of the case, Stella is stunned to discover Ellen had a secret friendship with Tom Knox and decides to pay him a visit.

Following Jean's shocking revelation, Calder sits on her fears about her father and Stella. However, when her secret background check on Amma returns a surprising link to Ellen Quinn, she must come clean to an unimpressed Tosh.

When secret letters signed off with the mysterious symbol are uncovered at the home of Tosh's prime suspect, the team ask if his pen pal might be an accomplice to murder.

At the same time, hospital security records bring one of Ellen's friends into the frame. Tosh and Calder track their latest suspect down to a remote location where they make a startling discovery.

Tosh visits the Sadats to ask if Ellen's struggles might be related to their son's death. They maintain that Ellen barely knew Akmal but, after Tosh leaves, Farida begins to unravel as her husband Azir watches on, concerned.

A voicemail from the night before turns suspicion onto Bobby Bain, but Tosh resists Calder's demands to make an arrest. When Sandy finds evidence of drug dealing at Cal's house, a defensive James points the finger at Neil Bain.

Tosh is accused of harassing the Sadats and Procurator Fiscal Harry tells her to back off. However, the warning only deepens Tosh's suspicion. Combing through the case files, she discovers evidence of a surprising connection between Heather Bain and the Sadats' family tragedy.
Later, a surprise confession reveals the shocking next step in the final movements of Ellen Quinn.

The farm is in lockdown and police search teams swarm over the property, as the Bains are rocked by Azir's revelation. Believing the identity of the killer lies in the reason why Ellen left Shetland, Tosh and Calder arrest Bobby Bain. An explosive interrogation does nothing to dampen Calder's suspicions.

Back at the farm, physical evidence of Ellen turns the spotlight on another member of her family, as the police continue to piece together her final movements.

As the Bains begin to unravel, Grace remains defiant, but her silence only serves to confirm the existence of a secret at the heart of this family. Piecing together all that they have learnt so far, Tosh and Calder move ever closer to an answer beyond what either of them could have imagined.