"It's absolutely typical of Harry. How anyone in his right mind can fall down a whacking great subsidence like that..."The Doctor decides to do a favor for the people of the Nerva Space Station, and beams down to Earth to check out if it's safe to re-colonize. Landing on an old teleport pad, the Doctor, Sarah Jane and Harry find a rather... smooth and barren Earth. The Doctor begins to tinker with the teleportation device as Harry immediately falls down a crevasse and vanishes. Sarah Jane goes looking around, wondering if she can find Trafalgar Square. Because, you know, the Doctor says they're actually in England. Again.As it turns out, however, it's not an abandoned Earth, as there are several random astronauts who decided to visit the Earth as well. One of them, Roth, is utterly insane... and, of course, he's the first one that Sarah Jane runs into. Luckily, Roth is one of the nice crazy ones and takes Sarah Jane over to the other astronauts, though won't go near them himself as he believes that the one named Vural is working with some random alien on the planet. Apparently, the astronauts are on the Earth because they received a distress signal — and once they landed, their ship was blown up by this alien wandering around.As it turns out, the Doctor also happens upon these astronauts eventually. And he's just alien enough to fit the bill of whoever has been stalking and even torturing these astronauts. So the Doctor runs away... only to fall down the same crevasse as Harry. Harry, for some reason, is nowhere to be found and is wandering around elsewhere. Meanwhile, crazy Roth and Sarah are captured by a completely random robot flying around, and are taken to the alien himself.The alien is, in fact, Field Major Styre of the Sontaran Military. Sarah Jane actually begins quaking in fear from this guy, remembering Linx from her first story... only to realize it's not the same guy. Shooting Roth dead, Styre takes Sarah Jane off to a random area and begins torturing her. The Doctor runs in, trying to save Sarah, but is quickly beaten and left for dead by Styre as he totes Sarah Jane off elsewhere. Harry, for his part, takes care of a dying random astronaut... who dies rather gruesomely of thirst shortly afterwards.In quick succession, Harry frees Sarah Jane from her bondage, the remaining astronauts are captured by Styre's robot, and it's revealed that astronaut Vural really is working with Styre in hopes of sparing his own life. Which doesn't work, as Styre now tortures all three astronauts. Because he needs to figure out the various resistances of humankind in order to report back to Sontaran Command on if Earth can be taken over easily. You know, despite it being abandoned. The Doctor finally shows up and challenges Styre to mortal combat, and the pair begin to fight. Vural dies trying to help the Doctor.Sadly, the Doctor doesn't beat Styre in combat, but he buys enough time for Harry to mess around with Styre's space ship. Battered but not defeated, Styre flees back to his ship to feed on energy ... only to randomly melt and explode from whatever Harry messed with. The Doctor then speaks directly to Sontaran Command and plays a few mindgames with them — convincing the Sontarans that the Earth isn't something to mess with right now. The day saved, despite only two of the original nine astronauts remaining alive, the Doctor and companions hop back in the teleportation pad to go back to Nerva Station and let them all know that the Earth is just fine and dandy now.
— The Doctor begins to despair of his new companion already.
This is only two-part adventure in the 1970s, which wouldn't happen again until "Black Orchid" in 1982.