The hills are alive with the sound effects. The Doctor appears on location. Then Harry appears in his duffle coat, and then Sarah appears in yellow and being upside down. The Doctor starts sonicing the balls they find there and sends Harry and Sarah away so he can be alone with his balls.
Harry, perhaps realising that this story is only half as long as usual so they have to get on with things, wastes no time in falling down a hole. Silly Harry.
Mannys with guns see the Doctor but decide not to shoot him. A robot comes and chases one of the mannys until he falls down and goes
The Doctor finds the body but then other mannys come and this time they do shoot him, with bullets that make him go to sleep.
Sarah shouts for the Doctor but he is not sonicing his balls where she left him any more so she can't find him. When she gets back to the hole she can't find Harry either, because he has found that the hole has a hole in it and has escaped that way.
Sarah is captured by a manny but he is friendly really because he helps her not be pounced on by the robot. This manny is Roth. Roth is very scared of the robot, and with good reason.
When he wakes up, the Doctor talks to the mannys who shot him. They all have great space names like Vural and Erak and Krans. They don't believe he teleported down from Nerva because they think Nerva is only a myth like Atlantis or the 1980s.
Vural - the leader of the mannys because he has the most space name - has a camera on him, through which the Doctor is being watched on TV by an alien. The Doctor is suspicious of Vural. Krans begins to believe the Doctor but Erak doesn't, he wants to kill the Doctor.
Roth distracts them while Sarah frees the Doctor, then Sarah leads them to the hole where Harry fell down. The Doctor goes down after Harry, then the robot comes and captures Sarah and Roth.
It takes them to a big metal ball where Harry is hiding nearby. The alien comes out of the ball and takes its helmet off. It is a Sontaran!
This revelation of the monster that was in the title of the story at the end of part one made me think for a moment that this might have been written by Terry Nation, but alas no. It was quite exciting, with everybody quickly getting captured or in trouble, and then having escapes, and a scary robot, so overall a good episode.