Another adventure for the intrepid time traveller. The Doctor (Tom Baker) and Romana (Lalla Ward) are holidaying in Paris when they stumble across the mysterious Count Scarlioni (Julian Glover) to steal the Mona Lisa. With the aid of inept detective Duggan (Tom Chadbon) they discover that the Count already has several Mona Lisas walled up in his cellar - all of them painted by Leonardo Da Vinci - and when the Doctor finds out that Scarlioni is also conducting time experiments he begins to realize that his latest foe is not all that he seems... Due in part to an independent television strike, this story achieved the series' highest ever viewing figures, with the final episode peaking at 16.1 million.