Private detective William Monk was approached by the wife of successful businessman Angus Stonefield, who one fine morning went to his office and did not return home. Monk immediately considered this case uninteresting - probably the missing man simply had another woman or he ran away due to financial problems. But Mrs. Stonefield said that, without a doubt, his twin brother Caleb, who led a completely insane life in the London slums, was to blame for Angus's disappearance. According to her, he always hated Angus, who had achieved so much in life, and often quarreled with him - and now, it seems, their next quarrel ended in fratricide. The detective began searching for Caleb, not suspecting what an amazing - and truly terrible - story he would learn...