Parts: 4
Writer: Terry Nation
Airdates: 23 February 1974 - 16 March 1974
Production Code: XXX

Doctor: third
Companion: Sarah

Creature Feature: Daleks, Exxilons

Story: The Doctor and Sarah are looking forward to a holiday on the rejuvenating planet of Florana, with its waters full of effervescing bubbles in which no-one can sink. Sarah is taking her water wings along, just in case. But suddenly, the TARDIS loses all power, just managing to materialize on a cold, dark, muddy, foggy planet. Even the torch that Sarah digs out fails, so the Doctor and Sarah are forced to open the doors with a hand-crank and explore the planet's surface with a mere oil lamp. Unless they can find the source of the TARDIS' power failure, they will be stuck on the planet forever.

When Sarah goes back to the TARDIS to change, the Doctor is attacked by one of the planet's denizens, an Exxilon, dressed in dirty rags. Sarah suffers a similar fate when, while searching for him, she comes across a glowing city towering above the rocky surface. The city is one of the Exxilons' sacred places, and anyone caught near it is condemned to be sacrificed.

The Doctor manages to escape from the Exxilons that captured him, and he eventually comes across a group of scientists and military officers from Earth, who have come to the planet in search of the mineral parrinium to cure a plague that is running rampant on the outer planets. They have been fighting off the Exxilons since they arrived, and to make matters worse, soon a shipload of Daleks arrives in search of parrinium, too. Their weapons are likewise useless, but they are concealing their true intentions, despite forming an alliance with the humans. Together, the humans, the Daleks and the TARDIS crew must work together to stop the power drain so that the parrinium can be delivered to those who need it - but the Daleks are already scheming of a way to control the parrinium supply themselves, and they do not intend to let anyone stand in their way.