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.