As DI Jimmy Perez investigates the murder of an elderly lady who is shot dead outside her croft, he finds evidence of a massive, bitter dispute between two families.

With two murders and no strong leads, can Perez apprehend the suspect before crowds descend on the Shetland Islands for Up Helly Aa, the biggest fire festival in Europe?

When the body of a teenage girl is found on a beach, DI Perez leads the investigation. It seems the case may be linked to the disappearance of a young girl 19 years earlier.

DI Perez believes he and his team are finally closing in on the killer as they discover what 17-year-old Catherine Ross was hiding from everyone in the hours before her death.

A journalist is killed in a road accident and it emerges he was an old pal of Perez. As the investigation progresses it seems the victim's return to Shetland was connected to plans for a controversial new gas pipeline.

After a second body is found brutally murdered, DI Perez wonders if the two killings are connected to corporate greed and corruption on the island or to just one woman - Evie Watt.

When a scientist is murdered in a bird sanctuary on Fair Isle and Perez returns to his childhood home to investigate, a storm forces Perez and the suspects to remain enclosed under the same roof.

Time is running out for Perez as prime suspect Peter Latimer lies critically ill in hospital. Was the fire a drunken accident, or was Latimer the second victim of a murderer still free on Fair Isle?

When a young man disappears on a ferry crossing and a small boy ends up in intensive care, DI Perez and his team become convinced the two events are connected.

DI Perez grows convinced that Maguire is implicated in the grisly death of a young man discovered in a shipping container.

Perez and Tosh's investigation leads them to Glasgow, where they hope to uncover the truth behind Maguire's death and his connection to Robbie Morton.

As the case gathers pace, Perez, Sandy and, most significantly, Tosh are all under threat.

Perez discovers that the person responsible for Robbie and Michael's deaths is closer to home than he had thought.

When Thomas Malone has his murder conviction overturned after 23 years behind bars, DI Perez has to reopen the investigation into the 1994 death of local teenager Lizzie Kilmuir.

Perez is on the trail of an attacker, Tosh investigates an oil company in the hunt for Sally's killer, and DNA testing in the Kilmuir case yields a surprising result.

Perez questions Donna about the DNA results, Tosh arrives in Norway in search of Andreas Hagan, and an unexpected twist leads Perez and Tosh into the murky world of the Norwegian far right.

Ignoring Norwegian secret service warnings to the contrary, Perez and Tosh track down Mathias Søderland, as the murder mystery continues.

Perez must reassess the investigation following Jo's attack, the MIT sets its sights on Malone, while Tosh grows skeptical of Lars.

Troubled by historical DNA evidence results, Perez has to face the fact that Duncan may have been involved in Lizzie Kilmuir's murder and potentially Sally McColl's as well.

Hoping to find information on Paul Kieran, Jimmy goes to Glasgow. There, he and DI Sam Boyd from the trafficking unit pursue some leads. Plus, Jimmy can't visit Glasgow without seeing Cassie, which brings her to the attention of the people tailing Jimmy and puts her in danger, too.

Having heard of the traumatic events in Glasgow, an angry Duncan confronts Jimmy over his fears for Cassie's safety. Cassie, although shaken, seems pleased that Jimmy has trusted her with the truth. Grant, young plain clothes officer, is tasked with keeping an eye on her. Now sure that Zezi is still being held on Shetland, Jimmy and Sandy pay a visit to Morag Dunwoody in an attempt to get more information from her. Her attitude has changed completely from the day before, when she admitted to Sandy that Calum didn't transport the girls to the mainland. Morag is obviously shaken and Jimmy suspects that she's been warned off by the traffickers. That night, Morag's home is set on fire, but she escapes, terrified, with her young children and later admits that she received a phone call before the attack, from a woman with a Glaswegian accent. Andrea Doyle, the tattooist, becomes a potential suspect. Very affected by his kiss with Alice, Jimmy tries to meet up with her, but the investigation keeps getting in the way. When he finally does get the chance to see her, Alice admits that she's not sure how she feels about the situation and whether she still loves Chris or not. While Duncan is out for a drink, he sees Jimmy and Alice chatting intimately in a corner - but so does Chris. Sandy pulls an all-nighter going through CCTV and tracks down Andrea Doyle at a gas station near the Dunwoody's house prior to the attack. They manage to find an address for her and she is arrested after a chase. Frustrated by not getting any closer to finding Zezi and convinced that Jamie Hayes knows more than he's letting on, Olivia ambushes Jamie and Rosie, and drives off with Jamie in the car.

The discovery of Nikki's body intensifies the search for Zezi. Perez feels that time is running out. A desperate Olivia tries to get information from Jamie Hayes.

Perez closes in on Zezi's location at last. But can he reach her before it's too late?

Alex Galbraith is shot dead on Pérez's mother's funeral. Their investigation is interfered by Fraser Creggan. A pipeline worker Eamon Gauldie informs Pérez that he has evidence on his drone that can identify Galbraith's killer.

Niven and Darren are arrested and brought to the station for interview. Perez finally brings the investigation to a climax - but he has no time to rest when it turns out Donna has one last surprise in store.

Perez issues a warrant for Connor's arrest and looks for the motive behind his bomb-making. Sandy tries to find out what business William Rodgers had in Shetland.

The team races to identify the killer and prevent disaster striking Lerwick. As the investigation draws to a close, Perez faces a life-changing decision.

Perez is on the trail of an attacker, Tosh investigates an oil company in the hunt for Sally's killer, and DNA testing in the Kilmuir case yields a surprising result.

Perez issues a warrant for Connor's arrest and looks for the motive behind his bomb-making. Sandy tries to find out what business William Rodgers had in Shetland.

Alex Galbraith is shot dead on Pérez's mother's funeral. Their investigation is interfered by Fraser Creggan. A pipeline worker Eamon Gauldie informs Pérez that he has evidence on his drone that can identify Galbraith's killer.

Troubled by historical DNA evidence results, Perez has to face the fact that Duncan may have been involved in Lizzie Kilmuir's murder and potentially Sally McColl's as well.

Ignoring Norwegian secret service warnings to the contrary, Perez and Tosh track down Mathias Søderland, as the murder mystery continues.

A journalist is killed in a road accident and it emerges he was an old pal of Perez. As the investigation progresses it seems the victim's return to Shetland was connected to plans for a controversial new gas pipeline.

Having heard of the traumatic events in Glasgow, an angry Duncan confronts Jimmy over his fears for Cassie's safety. Cassie, although shaken, seems pleased that Jimmy has trusted her with the truth. Grant, young plain clothes officer, is tasked with keeping an eye on her. Now sure that Zezi is still being held on Shetland, Jimmy and Sandy pay a visit to Morag Dunwoody in an attempt to get more information from her. Her attitude has changed completely from the day before, when she admitted to Sandy that Calum didn't transport the girls to the mainland. Morag is obviously shaken and Jimmy suspects that she's been warned off by the traffickers. That night, Morag's home is set on fire, but she escapes, terrified, with her young children and later admits that she received a phone call before the attack, from a woman with a Glaswegian accent. Andrea Doyle, the tattooist, becomes a potential suspect. Very affected by his kiss with Alice, Jimmy tries to meet up with her, but the investigation keeps getting in the way. When he finally does get the chance to see her, Alice admits that she's not sure how she feels about the situation and whether she still loves Chris or not. While Duncan is out for a drink, he sees Jimmy and Alice chatting intimately in a corner - but so does Chris. Sandy pulls an all-nighter going through CCTV and tracks down Andrea Doyle at a gas station near the Dunwoody's house prior to the attack. They manage to find an address for her and she is arrested after a chase. Frustrated by not getting any closer to finding Zezi and convinced that Jamie Hayes knows more than he's letting on, Olivia ambushes Jamie and Rosie, and drives off with Jamie in the car.

Hoping to find information on Paul Kieran, Jimmy goes to Glasgow. There, he and DI Sam Boyd from the trafficking unit pursue some leads. Plus, Jimmy can't visit Glasgow without seeing Cassie, which brings her to the attention of the people tailing Jimmy and puts her in danger, too.

Perez must reassess the investigation following Jo's attack, the MIT sets its sights on Malone, while Tosh grows skeptical of Lars.

Perez questions Donna about the DNA results, Tosh arrives in Norway in search of Andreas Hagan, and an unexpected twist leads Perez and Tosh into the murky world of the Norwegian far right.