Winter 1954. Professor Mortimer is attending a seminar at the Ashmolean Museum, the archaeological museum of the University of Oxford. There, the museum's curator asks for his help in solving several thefts committed by a figure dressed entirely in white. Meanwhile, Captain Blake is investigating the murder of two old study friends and uncovers a pattern that threatens two more of his friends. At first, there seems to be no connection between these two cases, but that is about to change...