Returning from holiday Hamish becomes unaccountably worried - it's as if he senses a dark cloud of evil hanging over Lochdubh. He soon learns that there is a newcomer to the village, a woman called Catriona Beldame, and that the villagers have decided she is a witch. At first Hamish is charmed by her, but is dismayed when he finds out she's been supplying dangerous potions to certain local people. No one seems willing to listen to his warnings and when she is found murdered, poor Hamish is the prime suspect.