29 September 1979
Julian Glover (Count), Catherine Schell (Countess), Tom Chadbon (Duggan), David Graham (Kerensky), Kevin Flood (Hermann), Pamela Stirling (Louvre Guide) [1, 3], Peter Halliday (Soldier) [2-3], Eleanor Bron, John Cleese (Art Gallery Visitors) 
|Written by||David Agnew|
|Directed by||Michael Hayes|
|Produced by||Graham Williams|
|1||“Part One”||24: 25||29 September 1979||12.4m|
|2||“Part Two”||24:33||6 October 1979||14.1m|
|3||“Part Three”||25: 25||13 October 1979||15.4m|
|4||“Part Four”||25:08||20 October 1979||16.1m|
The Doctor and Romana are enjoying a well-earned break in Paris, relaxing in the gentle delights of the art galleries, the waterfront cafes, the Eiffel Tower… and the unexpected jumps in time that no one else seems to notice… Rare treasures and once-lost masterpieces are suddenly in auction houses all over the world, the only link to them all being the mysterious Count Scarlioni.
But what project is he secretly financing in the basement of his Paris chateau? The time-travellers meet up with Duggan, a private detective investigating the activities of the Count and his accomplices. Can Scarlioni be planning the most audacious and daring of all art thefts? Or are his ambitions much grander? Big enough to threaten the existence of the entire human race…?..
After The Reign of Terror and The Massacre of St Bartholomew’s Eve, this was the series’ third story to take place primarily in and around Paris.
“David Agnew” had written once before for the series, in The Invasion of Time, where the pseudonym was used to hide the identities of Graham Williams and then-script or Anthony Read.