While sightseeing in Paris, the Doctor and Romana find themselves repeatedly reliving the same moments in time. A visit to the Louvre Museum leads the Doctor to suspect an alien plot to steal the Mona Lisa.
As time slips a groove, the Doctor and Romana relive twenty-four seconds while on holiday in Paris. The second time it occurs the Doctor spots a woman using advanced, alien technology at the Louvre to study the security system guarding the Mona Lisa, but it's the Doctor who falls under suspicion of being a clever and masterful international art forger.—statmanjeff