With two people dead and no strong leads, Perez is under great pressure to catch the killer before tourists descend on the islands of the Up Helly Aa festival.
Having initially thought that Hattie’s death was suicide, Perez is now troubled by it, he is convinced that the defence wounds on her body suggest a more sinister occurance.
When Gwen, Hattie’s mother, tells Perez that her daughter had a breakdown as a result of a bad love affair, Perez, Tosh and McCabe strongly believe than her supervisor, Professor Paul Berglund, is hiding something of vital significance – particularly as the murder weapon has his initials on them.
With his efforts to cancel the Up Helly Aa festival all but doomed, Perez is forced to conduct his investigation at the same time as a growing number of tourists descend on the island.
Perez decides to focus in on the Haldanes, and discovers than the root cause of Ronald Haldane’s alcoholism is his illegal gambling debts. Jackie Haldane, frustrated at the polices scrutiny of her son, voices her frustrations, while daughter-in-law Anna has some secrets to hide of her own.
While Sandy’s father still remains inscrutable, Perez probes the history of the Wilson family, finding what could be a link to the skull fragments found on murdered Mima’s land, and unearthing very long, well kept family secrets.
Whilst on a visit to see Vicky Kirkland at the Lerwick Museum, Perez and Tosh notice a vintage photograph of a very young Mima wearing the Freya goddess of love pendant that she gave to Hattie just before her death.
As Perez just begins to discover the answers to his difficult questions, the race to find Hattie and Mima’s murderer quickens. Through the crowded, torch glowing streets of Up Helly Aa, Detective Perez must find the murderer before anybody else is struck down.
Tonight, BBC One, 9pm. Leave your comments below.