The Doctor, Ian and Barbara arrive on the planet Dido where a crashed spaceship with the only two survivors are terrorized by the monsterKoquillion. But who is Koquillion? But the enemy may be closer then they think...

Landing in Rome, A.D. 64 the travellers take a rare holiday. While Ian and Barbara are happy to relax, the Doctor and Vicki set off to pursue adventure.

However, adventure soon finds Ian and Barbara too as they are kidnapped by slave traders, and the Doctor's imitation of Maximus Pettulian sees him taken to the court of Emperor Nero where he inadvertently plays a part in deciding the course of history...