In a small island off the American coast, the Whateleys live in an old mill where a mysterious bloody being creates an atmosphere of horror. After her parents get killed by lightning, young Susannah is sent to New York by her aunt Agatha, who wants her to avoid the family curse. Years later Susannah, now married, persuades her husband to spend a holiday in the abandoned mill. Once on the island, Susannah and Mike soon find themselves exposed to the hostility of a gang of thugs led by Ethan, Susannah's brutal cousin.
Gig Young
as Mike Kelton
Carol Lynley
as Susannah Whately Kelton / Sarah
Oliver Reed
as Ethan
Flora Robson
as Aunt Agatha
Judith Arthy
as Emma
Ann Bell
as Mary Whately, Susannah's Mother
William Devlin
as Zebulon Whately
Charles Lloyd Pack
as Barge Master
Bernard Kay
as Tait
Rick Jones
as Luther Whately
Celia Hewitt
as Aunt Sarah
Robert Cawdron
as John Whately, Susannah's Father
