The Loch with subtitle

A community is nourished and sustained by myth, and bordered by untamed nature. There, the search for a serial killer becomes a matter of life and death for local detective Annie Cathro who is trying to cope with her first murder case. The proceedings kick off when the body of a local man is found at the foot of Carn Mohr Mountain and an isolated human heart on the loch shore. The town's normality is shattered as several local characters come under suspicion with the murderer lurking in their midst terrifying and rocking the village to its core. The central story revolves around Annie and her family whose stability is undermined as tensions stemming from the investigation threaten to disrupt and destroy their lives together.

A human heart is discovered on the shores of the Loch, and forensic psychologist Blake Albrighton is brought in to join the investigating team. He quickly forms a disturbing theory about the motive behind the seemingly inexplicable murders, but Chief Inspector Frank Smilie is quick to dismiss his ideas. However, if the new arrival is correct, the once peaceful Highland community could be set to endure far more deaths, as a serial killer prowls the area.

The police hold an appeal for the safe return of Jonjo. Anxiety is exacerbated by the fact that Jonjo suffers from bipolar disorder and has neglected his medication.

As Annie becomes more entrenched in the investigation, Alan feels increasingly marginalised and their relationship begins to suffer. College Principal Craig Petrie is questioned as the main person of interest. Petrie is connected to both victims, but he also throws doubt on Leighton's alibi during the time of the murder and Annie is forced to investigate. Other lines of enquiry include the stolen van in which the body was found. When a hair is discovered in the van, one not belonging to the victim, the hunt to find the driver escalates… As evidence mounts against Petrie, Quigley agrees to allow Albrighton into the interview to help crack Petrie's composure. But things take a downward spiral when Petrie turns the tables on Albrighton, goading him about a personal tragedy. Albrighton assaults Petrie leaving Quigley with no choice but to release the prisoner.

Craig Petrie visits Dessie to remind him the college trip to the hydroelectric dam is still on. Dessie's mother Mhari has doubts. Petrie insists it will do the kids good. Kieran arrives at Dessie's as Petrie is leaving. He agrees to join the excursion. In the investigation, Marr continues to be a person of interest and when a police search warrant is granted and his house and possessions are pulled apart, he finally snaps and goes after Evie, to put an end to what he sees as her campaign of hatred. In doing so, his secrets are revealed..