Slap bang on the border between the known universe and the realm of anti-matter lies the planet of "Zeta Minor". That's where the "Doctor" (Tom Baker) and "Sarah Jane" (Elisabeth Sladen) have to go to answer a distress call - and where they discover a professor "Sorenson" (Frederick Jaeger) who thinks he's found the ultimate solution to the energy crisis. Sadly, though, when they try to leave the planet they go nowhere fast. It seems that this energy has no intentions of leaving it's home world. Indeed, the more exposure the scientist has to this power source, the more malevolent it's influence...