With her daughter Evie's involvement in question, Annie is off the case. Jonjo witnesses Dr. Marr with a suspicious bag and then disappears, leaving his parents distraught. Forensic psychologist DCI Quigley believes finding the owner of the heart will lead to the killer. The danger in the town is growing as forensics reveal that there may be a second victim.

The police hold an appeal for the safe return of Jonjo. Annie and DCI Quigley interview Dr Marr and it's clear he has something to hide. Evie confides in her mother about Jonjo but takes matters into her own hands and breaks into Dr Marr's house. Her suspicions around Marr escalate and the desperate search for Jonjo and the killer continues.

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 with his connection to Niall Swift and Jonjo.

Dr. Marr's secrets and those of the McGrellish family are revealed and Evie finds out the truth of what's happened to her friend Bethan McGrellish - it is not what she expected. Just as the police think events at the dam have brought the case to a close the underwater drone on Alan's boat makes a huge discovery.

Quigley and Annie watch the body being pulled from the water. A photograph in the dead man's wallet links him to someone we know in Lochnafoy and ultimately directs Annie to the one person who can provide them with the final clue, leading to the killer.

Get some insight into the making of Loch Ness through these cast interviews.

Go behind the scenes with the cast and crew of Loch Ness.