Despite trying to land in Hyde Park, the Doctor finds himself on a world ravaged by the bitter war between the Sevateem and the Tesch. He soon meets Leela, an exile from the Sevateem village who immediately refers to the Doctor as "the Evil One." After being captured by the Sevateem several times, he deduces that the problems of this world have their root cause in his own previous intervention with their tribal god, Xoanon. Can he repair the damage? Will the Tesch ever stop bowing? Will Leela become queen of the Sevateem or join the Doctor in his journeys through time and space?
It's probably the later.
Justin and Erik discover the probable secret origin of the phrase "Tread Perilously." Erik explains Leela's murderous streak while Justin expounds on the virtues of space cavemen. They advance the theory that script editor Robert Holmes rewrote much of the story and highlight several Holmesian lines of dialogue. Justin also reveals whether or not he thinks "The Tomb of the Cybermen" continues to be the best of the tread safely Doctor Who episodes.