On a planet of primitives, there are human researchers who are unaware of the invasion of Tegan's mind by the Mara, a snake like being who wants to bring about the end of the mortal universe. Adric is once again used by the mad leader of the humans--mad due to the Kinda box and the Mara. When it is revealed Adric is helping the Doctor, the leader prepares to torture him. Adric escapes and gets into one of the TSS machines. The Doctor figures a way to exorcise the Mara from Tegan, get Adric out of one of the machines of the humans, and rid the world of the Mara. 25th Century or 31st Century. 2782.