The body of a young woman is washed up on a popular beach in a small coastal town in NSW Australia; her injuries are consistent with murder.
Detective Chief Inspector John Macgregor has been seconded to the area and brought in to investigate the case, a poker playing, hardy and dour Scot.
A prominent local Surgeon Dr Parranjoy Panngesh is under suspicion, Sergeant Cameron Fowler, Macgregor's young and ambitious partner, unravels the surgeon's murky past, his investigations uncover a history of corruption in Mumbai.
The girl's identity takes Macgregor to the town of Dubbo. He is welcomed by his old friend and colleague Mike Willoughby but soon encounters a close-knit, tight-lipped community unwilling to reveal information pertaining to the girl's death.
The girl's employer Dr Patrick Elliot a vet and the last person to see her alive is under suspicion as Macgregor uncovers his involvement in a secret cult of satanic worshipers.
Macgregor sets out to investigate him and a previous boyfriend of the girl, both have links to Dubbo plains zoo.
Gunner Adams, a killer and member of an outlawed biker gang, escaped from Goulburn Gaol and on the run from police. There is a history between them; Macgregor had been the detective that had him convicted of a double murder twenty years before.
Gunner seizes the opportunity for revenge when he catches site of Macgregor, following and attacking him. Macgregor recovers from the assault only to have Gunner attack him again days later. This time a lethal fight ensues; Gunner is fatally wounded.
Sergeant Fowler is requested to assist Macgregor in Dubbo following the failure to detain and arrest Dr Panngesh. He is asked to investigate a colleague of the murdered girl. He does not return from the interview and goes missing.
Another body is found, another investigation, Macgregor knows the victim terrified that his sergeant will be next.
A cryptic message over the radio leads Macgregor to the' Devils hole'. Macgregor waits, watching as members of the secret cult meet and begin their rituals, his Sergeant - drugged, the next victim.
Macgregor is alone and desperate for backup. Time is precious if he is to save Fowler's life, he attempts to rescue him but is discovered by the members of the cult. To survive he must stall them until help arrives. Willoughby storms in to rescue Macgregor. The Priest and his cult members are arrested, a semi-conscious Fowler taken to hospital. Macgregor uncovers the truth on interviewing the Priest, his childhood plagued with violence and sexual abuse by Christian brothers in a notorious Victorian orphanage. Dr Elliot's insatiable sexual and predatory behaviour are revealed, his role in the murders and his links with the Priest.
The truth and the secrets are out 'Down in the Devils Hole.'
