Melinda's mysterious new neighbor is haunted by an old classmate's dead grandfather, who suspects Tom kidnapped and killed his granddaughter.
The Doctor, Ian and Susan discover that they have exposed to radiation.
Barbara realises how to control the Robomen and orders an attack on the Daleks.
While on holiday in Paris, the Doctor and Romana experience a time distortion. At the Louvre, someone is taking an unusual amount of interest in the Mona Lisa.
The Doctor and Romana become the reluctant guests of Scarlioni who is planning to steal the Mona Lisa despite having six Mona Lisas hidden in his cellar – all of them genuine.