On a barren planet, an enormous tracked vehicle makes its way across the surface, scooping up sand. Humanoid robots man the command center and tend to the crew, which relax in luxury. One of the crew, Chub, teases the others by suggesting the robots might go out of control, but the others assert there's no way robots can go out of control given their safety overrides. The robots notify the crew they've spotted something and they head for the bridge.
Aboard the TARDIS, the Doctor is attempting to explain that there's no such thing as magic and how the TARDIS is interdimensionally transcendental. It doesn't go well, but they're interrupted when the TARDIS materialized in a metal storage bay. The Doctor takes Leela out to explore.
On the bridge, Uvanov leads his crew in pursuit of lucanol in the sand. In a storage bay, Chub goes to get a signal pack, finds that it's stuck, and calls for a robot. A robot with red glowing eyes comes in and strangles him and he screams, as outside Poul hears his cry.. One of the robots reports an obstruction in the forward vents.
The Doctor and Leela are in the vents and see that they are on a vast vehicle in the middle of a sand storm. They are unaware that a robot has lowered a servo arm and removed the TARDIS from its landing spot.
Poul reports that Chub is dead and Uvanov reluctantly calls off their hunt for lucanol. This inadvertently saves the Doctor and Leela, who realize the sand will cut them apart when it comes in through the vents and see the TARDIS has been removed. Uvanov and Poul check out Chub's corpse and find a "corpse marker," used to mark deactivated robots. Uvanov calls for a meeting of the human crew. He interrogates the other crew but no one has a solid alibi
The robots remove the Doctor and Leela from the storage bay and take them to the commander's cabin. They discuss what's happening while outside, one of the robots, V9, secretly listens in. SV7 then comes in to interrogate them, without any luck. After it leaves, locking them in, the Doctor sabotages the door and they slip out to find the TARDIS and look around.
Uvanov is told about the intruders and concludes they're the murderers, but at least some of the crew aren't so quick to dismiss the matter. Uvanov orders them to work but they refuse until Dask supports his case. The robots tell them that the intruders have escaped and Uvanov orders a general alert.
Leela slips away behind the Doctor and finds Chub's corpse, while the Doctor locates the TARDIS and then an empty storage bin with a corpse inside. He goes in to investigate and someone closes the door behind him, as sand starts to pour in, burying him…