Piano teacher Niall Swift is found dead at the bottom of a cliff by local schoolteacher Craig Petrie. Having been fired by local doctor Simon Marr just hours before his death, Swift's tragic end is initially deemed as suicide, until pathology discover that part of his brain was removed while he was still alive. Meanwhile, a schoolboy prank undertaken by a group of local students, including Annie's daughter, goes horribly wrong when the amongst the animal bones and offal used to try to recreate 'Nessie's corpse', a human heart is discovered. Realising that the team are dealing with a serial killer, DCI Lauren Quigley is seconded in to lead the investigation, alongside psychological profiler Blake Albrighton.