“Planet of Evil” is an adventure of the thirteenth season of “Doctor Who” classic series which aired in 1975. It follows “Terror of the Zygons” and it’s a four parts adventure written by Louis Marks and directed by Rodney Bennett.

The Fourth Doctor (Tom Baker) responds to a distress call and takes the Tardis to the planet Zeta Minor. There, he and Sarah Jane Smith (Elisabeth Sladen) find that the members of a Morestran scientific expedition were almost all killed. Only the expedition’s leader, Professor Sorenson, is still alive and thinks he’s on the verge of crowning many years of research on a new energy source.

A Morestran military starship arrives on the planet Zeta Minor shortly after the Tardis and the commander thinks that the Doctor and Sarah Jane have killed the members of the scientific expedition. The story gets even more complicated because the planet is on the edge of the known universe and beyond that there’s a big danger.