Inspector Maria Vern arrives on the island of Gotland for a vacation. But instead of a leisurely part-time job at the local police station combined with rest by the sea and walks through the ancient town of Visby, she and her colleagues face busy days ahead: a recently murdered man's body has been discovered in an ancient stone burial mound. The deceased, Wilhelm Jacobson, turns out to have been a difficult man. But who could have wanted him dead? And is there a connection between his death and two other murders, the mysterious marsh lights over Martebo, and the legendary silver of a medieval Danish king?