Wilke Collins was the author of two of the greatest mysteries ever written, The Moonstone and The Woman in White. However, like Poe before him and Conan Doyle after, he shifted easily from rational domains to the 'superrational'. Like them, he often preferred to indulge his occult predilection, a lifelong indulgence. His last lucid effort in this area (before ill health and opium drained his powers) was this short novel, written in 1878. In it, he artfully combines elements of both the detective story and the supernatural.