Dr Oldfield finds himself caught one night in a police hunt. When he stumbles upon a policeman struck dead by an unknown assailant, Oldfield determines to piece together what happened. What unravels is a story of ingenious theft involving diamonds and the remains of an artist's body found in a kiln. Oldfield engages the help of Dr Thorndyke and together they trace the work of the artist and a valuable stoneware monkey that hides an incredible secret.