It's summer on Gotland and an international group of archaeology students are excavating an ancient Viking site. The camaraderie and holiday spirits of the group are shattered when one of their number, a Dutch student called Martina, disappears. Rumours abound about a secret relationship she was having with someone on the island, but is her disappearance simply a lover's intrigue? When the body of a horse is discovered in a local farmer's field, other rumours begin to circulate.The horse had been decapitated and the head has vanished. Why would someone take a dead horse's head? As Inspector Knutas begins his investigation, echoes from Gotland's Viking past begin to trouble his search. When Martina's naked body is found hanging from a tree, with what look like ritualistic markings on her skin, there can be little further question. Someone is calling to the old Gods of Gotland. Martina has been killed according to the Viking ritual of the three-fold death, and the one thing the ritual points to is that more deaths will follow.