FOR A PRIVATE INVESTIGATOR LIKE DUGGAN, being sent to Paris certainly makes a change from divorce enquiries. Duggan has been hired to find out why priceless art treasures missing for centuries are suddenly appearing on the market. It soon becomes clear that the world-famous Count Carlos Scarlioni is behind this uproar in the art world. While watching Scarlioni’s Countess and her heavies studying Leonardo da Vinci’s famed Mona Lisa in the Louvre museum, Duggan collides with the Doctor. The latter is holidaying with Romana in spring 1979 and has just been affected by a time slip.