The Doctor and Romana's search for the fourth segment of the all-powerful Key to Time leads them to the planet Tara, where courtly intrigue and romantic pageantry employ the most sophisticated technology.

Within hours of arriving, Romana is mistaken for a powerful princess and the Doctor forced to dally with robotic royalty - and both are quickly embroiled in the scheming ambitions of the wicked Count Grendel. Finding the segment of the Key is easy enough, but escaping with it in one piece will prove an altogether more colourful affair...