Planet of the Daleks

From http://www.bbc.co.uk/doctorwho/classic/episodeguide

The TARDIS materialises in a hostile jungle on the planet Spiridon. Jo sets out alone to find help for the Doctor, who has fallen into a coma. She meets a party of Thals and is left in hiding aboard their crashed spaceship while they go to the Doctor's aid. The Time Lord, now recovered, learns of their mission to destroy a party of Daleks sent here to discover the native Spiridons' secret of invisibility.

Another Thal spaceship crash-lands in the jungle, and the survivors bring news that somewhere on Spiridon there is an army of ten thousand Daleks. Jo meanwhile meets a friendly Spiridon named Wester, who cures a deadly fungus disease that she has contracted.

It transpires that the Daleks' army is frozen in suspended animation in a cavern below their base. The Doctor, with the help of the Thals, explodes a bomb in the cavern wall and thereby causes one of the planet's natural ice volcanoes to erupt, entombing the army in a torrent of liquid ice.

The newly-arrived Dalek Supreme and his aides are left stranded on Spiridon as the Thals steal their ship and the Doctor and Jo depart in the TARDIS.

16 out of 31 (51.6%) raters say this story requires a previous story.