A painting of masked revelers at the Venice carnival has a secret: to stare into the painting is to play dangerously with the unseen demons it hides, and become the victim of its macabre beauty.

An inveterate traveller, Sir James Monmouth has spent most of his life abroad. He arrives in England on a dark and rainy night with the intention of discovering more, not only about himself but about his obsession with Conrad Vane, an explorer. Warned against following his trail, Sir James experiences some extraordinary happenings.