Dr Edward Carstairs, a noted psychologist, is called in to investigate the case of Sir Arthur Carmichael, a young man of twenty-three who woke up the previous morning at his estate in Herefordshire with a totally changed personality. Carstairs travels down there with a colleague called Dr Settle, who tells him that he feels that the house could be haunted, and that this phenomenon has connections with the case. The household consists of Sir Arthur, his stepmother, Lady Carmichael, his half-brother of eight years of age, and a Miss Phyllis Patterson to whom Arthur is engaged to be married. As their horse carriage comes up the drive, they see Miss Patterson walking across the lawn, and Carstairs remarks on the cat at her feet which provokes a startled reaction from Settle.