The plot of his illegitimate son Mordred to gain the throne, and Guinevere's growing attachment to Sir Lancelot, threatens to topple King Arthur and destroy his "round table" of knights.

The lives and passions of a stock car team are revealed against the turbulent backdrop of the professional racing world.

The Doctor, Ian, Barbara and Susan arrive in the TARDIS on board a spaceship. Their initial concern is for the ship's human crew, who are suffering from telepathic interference from the Sensorites, but Susan communicates with the Sensorites and finds the aliens fear an attack by the humans and are just defending themselves. Travelling to the Sense Sphere (the Sensorites' planet) the Doctor seeks to cure an illness to which the Sensorites and Ian have succumbed, but finds it has been caused by deliberate poisoning. The political manoeuvring of the Sensorite City Administrator poses another threat to the TARDIS crew as he seeks to discredit and implicate them.