The frontier is closing, but the imagination of the west remains. Decades since the genocide of a local tribe, there is one final 'wild-man'. Benjamin wishes to rid the land of the indigenous peoples, tasking Henry with extermination.

The Doctor and Peri arrive on Karfel, a planet ruled by fear where the enemies of its ruler, the despotic Borad, are banished into a time tunnel known as the Timelash.