East End landlady Mrs Drabdump is alarmed when she cannot rouse her lodger Arthur Constant. She summons the assistance of her neighbour, retired Scotland Yard detective George Grodman. He breaks down the door, only to find the man lying dead on his bed, with a deep cut to his throat. No-one could have got in or out of the locked room and there is no sign of the murder weapon. Who was the killer and how will he be identified? When a man is condemned to death for the seemingly impossible crime, Grodman is unconvinced that he is guilty.