The Doctor has been framed as the monster maker by Finch and is on the run from the army, while Sarah attempts to alert UNIT to what Grover is up to.

As the TARDIS heads to the paradise planet Florana where the Doctor and Sarah go for a holiday, the TARDIS goes off-course and arrives on the barren planet Exxilon, where the TARDIS is loosing power. The Doctor and Sarah finds a group of humans and Daleks are searching for Parrinium, a mineral which is the only antidote to a space plague. Both parties encounter the native people and trouble ensues. In an attempt to find what caused the power-loss, the Doctor, chased by the Daleks, enter the Exxilon's lost city to be able to stop the power draining phenomenon.