In the bleak winter of 1741, in the isolated village of Glenboyne, a series of horrific murders occur in the Dublin mountains. Daniel Pearsons, an English official, is dispatched from Dublin Castle to investigate the crimes, and finds a community in the grip of terror, and unwilling to talk. What should he make of the rumours of a demonic creature sworn by the locals to be seen and heard at the scene of each killing? And why do bonfires light up the midnight sky at the summit of the mountaintop? But the truth is darker than he could have imagined.