When Mr Mummery took the morning train down to his business as he always did, and opened the door of his office as he always did, and saw his partner Brooks sitting at his desk as he always sat, the world seemed perfectly orderly and dependable and sane. But then it began - very simply - out of a few chance remarks, and the terror took shape and grew, until it was a black mountain of fear and suspicion! Ed Mummery has begun to suspect that his housekeeper is trying to kill them...