Craeghatir: a lonely rock, far out on the northernmost tip of Britain; the closest point of land to it, the wild, storm-ravaged Cape Wrath. To call this place bleak is the understatement of a lifetime. Huge cliffs dominate its shores, but within there are green tracks linking secret valleys where tumuli can be found, ancient megaliths and the bones of prehistoric mammals long grown over with moss. The island is now uninhabited and in terms of this beauty and silence, it is an outstanding locale - though few sightseers ever venture there willingly, for Craeghatir has an evil reputation. Professor Jo Mercy of Warwick University's elite archaeological unit doesn't believe the rumours and is keen to investigate a newly-discovered barrow on the island which might contain the remains of Ivar Ragnarsson, perhaps the most infamous of all Viking chieftains. Ragnarsson was reputed to be berserkir - a warrior possessed with the wolf-spirit, whose madness carried him past all pain and reason in the heat of battle, and whose victims were deemed offerings to the wolf-god Fenrir. But Mercy and her team will find themselves faced with more than just the inhospitable environment on Craeghatir, as the spirit of Ragnarsson is disturbed and death and madness come to the island.