27 October 1750: A boy runs breathless on a dark autumn night. The letter Bishop Matthews' deacon has to deliver to Arthur William Harrington, an aristocrat and secret member of the Ambactus Danu sect, contains news that could upset the peaceful existence of the Greystone people. A terrible and evil force is awakening and threatens to bring death and terror on the night of Samhain. To prevent evil from reaping its victims, the four masters will have to perform an ancient ritual that will imprison the beast and plunge it back into the underworld.

20 October 1884. Scotland Yard Inspector Dorian Bayley is sent to the remote town of Greystone in the north of England to investigate the theft of an ancient manuscript and the mysterious disappearance of local inspector Nevil Morgan a few days later. As soon as he arrives in the village, however, the inspector learns that a horrendous murder was committed inside the church during the night. The rationality with which Dorian Bayley will conduct the investigation will soon clash with the beliefs and superstitions that envelop Greystone and affect the lives of its inhabitants.

A detective story that weaves past and present in a complex game of puzzles that will bring to the surface a surprising truth, veiled by the thousand mysteries that grip Greystone, where the border between rational and supernatural blurs into a vision of horrific and ambiguous reality.