Doctor Who: Full Circle

The TARDIS falls through a CVE into E-Space and arrives on the planet Alzarius. There the inhabitants of a crashed starliner and a group of young rebels called the Outlers, led by a boy named Varsh and including his brother Adric, are terrorised by a race of Marshmen who emerge from the marshes at a time known as Mistfall. The Doctor discovers that the starliner's inhabitants are not the descendants of its original crew, as claimed by their leaders, the Deciders, but evolved Marshmen. With the Time Lord's help and encouragement, the starliner is repaired and able to leave the planet.