Episode list

Whist detective sergeant Annie Redford and husband Alan are at a curling match, their daughter Evie and her friends, Jonjo and Kieran, create a hoax construction of the Loch Ness monster to boost Alan's business taking tourists round the Loch. Annie is called in to investigate, but finds herself on her first murder case after college lecturer Craig Petrie finds the corpse of gay piano teacher Niall Swift. Part of the victim's brain has been removed. To the annoyance of Annie's superior Frank Smillie, DCI Lauren Quigley is brought from Glasgow, along with forensic psychologist Blake Albrighton. When a human heart is found in Evie's fake monster, which the youngsters deny all knowledge of seeing, Blake believes a serial killer is at work. However Annie is compromised by Evie's actions and taken off the case.

Petri throws a phone, possibly the victim's, into the loch. Lauren's key suspect is Leighton Thomas, on life licence for a 20 year old murder, but she also believes Craig is hiding something. A dead wolf, released from its sanctuary by Jonjo, is found at his father's abattoir, increasing animosity between Lauren, who orders its closure, and Frank, whilst Annie learns that unpleasant doctor Simon Marr, who sacked Niall for exposing his daughter to music he deems offensive, owns to running the wolf over and asking for its incineration at the abattoir. Annie impresses Blake when she finds brain fragments in a cairn, and he persuades Lauren to reinstate her. Lauren believes she has found a clue to the killer's identity in a newspaper found near Niall's corpse. Meanwhile Evie and Kieran are run off the road by a mysterious driver, and Jonjo goes missing.

At an appeal for the missing Jonjo, Blake causes chaos by announcing that a serial killer is at large, and Lauren must step in to prevent his removal from the case. After Evie and Kieran have told the police about their ordeal, and suspicions about Simon Marr following a text from Jonjo, Evie makes a discovery when she illegally enters the doctor's home, whilst a house to house reveals that Kieran's soldier brother Jordan is being kept alive in a comatose state by his family. Blake believes handwriting found on a newspaper next to Niall's corpse will be that of the killer, and organizes a village meeting where all male residents are asked to sign in, but it is interrupted when Annie finds Jonjo's dead body.

Following Jonjo's murder Craig is questioned, since his handwriting matched that on the newspaper found near Niall's body. Videos on the computer in his locked room show him counselling students, which Blake attributes to his controlling personality, though Lauren is less sure. Craig mentions seeing Leighton when he discovered Niall, but Leighton has another problem - the reappearance of his knife-wielding ex-cellmate Oliver Tench. Alan learns about Leighton's criminal past, putting him in danger from which Annie and Leighton rescue him. Meanwhile Craig is blackmailed over a possible affair with Niall, Jordan recovers, and Annie believes she has found the owner of the van in which the dead Jonjo was found.

Blake is taken off the case after assaulting Craig, who is also targeted by a gunman, possibly student Dessie Toner, his suspected blackmailer. After Mair's house is raided Evie uncovers his relationship with Bethan McGrellish and the secret they are sharing whilst Lauren believes the suspect seen on CCTV is actually not the killer but their first victim. Annie finds weapons possibly used by the murderer at the same time that Craig is taking his students on a tour of a hydroelectric dam. She joins Lauren as they pursue their suspect along its darkened corridors, finding other bodies on the way. Alan, returning to work, finds another corpse in the loch. Toner is the chief suspect as the killer but the dismissed Blake tells Lauren he believes he was not acting alone.

Annie is in desperate pursuit of the killer as he closes in on his latest victim.