After visiting scientist Anna Blake is found murdered in her lab, Perez is compelled to return to his childhood home of Fair Isle. The only suspects appear to be Anna's immediate family and Anna's fellow scientists. Perez and Tosh arrive just before the flights to and from Fair Isle are grounded, due to storms over Shetland. They will have to work in isolation, without access to a forensic team. Perez works quickly, ensuring the crime scene is sealed off. He sends photos of Anna's body to Sandy, who sends them on to forensics in Scotland in order to find a probable cause of death. Meanwhile Tosh is out searching for Peter Latimer, a resident scientist who has been missing since Anna's body was found. She finally apprehends him and brings him back to the centre. Perez decides to leave Latimer on his own for a while as Tosh searches his room looking for anything that connects him to Anna's death. Perez then interviews Anna's husband, Frank.

Frank is distraught but increasingly agitated by Perez's questions, especially over the fact he and his wife slept in separate rooms. When Perez finally speaks to Latimer, rather than provide evidence to back up his alibi, Latimer instead demands a solicitor. Latimer has become the prime suspect, particularly when Sandy finds out that he and Anna had a secret assignation in Lerwick two weeks previously. But when Finlay Caulfield is caught trying to damage a memory card from his camera, Perez quickly discovers that all of the pictures on it are of Anna Blake and that Finlay has form for harassment. Armed with this information, Perez goes to speak to him, but Finlay has disappeared from the Field Centre. As Tosh searches for him, a huge explosion is heard nearby. Perez and Tosh swiftly drive towards the source of the blast. They are horrified to see a man on fire running from the burning bird hide. Perez uses his coat to put out the flames. It is Peter Latimer...