Paris, 1979. The Doctor and Romana are here on holiday, but something is disturbing the flow of time. Could the time travel experiments of Count Scarlioni be to blame?

Captured by the Count, the Doctor and Romana uncover an elaborate plan to steal the Mona Lisa. But there is more to Scarlioni's plans than a simple theft.

The Doctor and Romana unwrap an intricate plot involving aliens, time travel and the Mona Lisa. How is Count Scarlioni living in two times at once? And what does he want?

Scaroth is determined to go back 400 million years in time to prevent a mistake. But the Doctor must stop him – because the consequences would be disastrous.