The Doctor produces a snorkel from his pocket. Robots come in to remove Chub's body while Leela hides, then follows them after they leave. Ignoring Uvanov, the crew decide to help the robots with the search and split up.
A robot notes impurities in the bay, drains off the sand, and releases him. The Doctor tells the robot about the dead man, Kerril, and it takes him into custody. Leela returns to the commander's quarters to find Leela and sees something moving in a covered alcove. She investigates and finds the dead body of a crew man, Cass. A "dumb" robot, D84, approaches Leela and asks her not to cry out, saying it can't be found there. It points out that if it had killed Cass, it would kill Leela as well, then releases her. It asks her if it knows what the corpse marker is, then asks her not to reveal its existence. D84 grabs her as Uvanov comes in and slaps Leela around, and she kicks him in response. She protests her innocence and when she asks D84 to defend her, Uvanov points out it is a "dumb" model. they're interrupted when Poul comes in to tell them they've caught the Doctor, who they assume killed Kerril. Leela is taken out, protesting her innocence, and Poul secretly agrees with her.
Uvanov interrogates them and the Doctor says they're innocent, pointing out that someone tried to kill him to divert suspicion. It doesn't go over well and Uvanov has them locked up. After they leave, Uvanov talks to Zilda and suggests he'll have enough money to reinstate her family's fortunes, but she leaves in disgust.
In a far corner of the cargo bay, a human figure gives a corpse marker to a robot with orders to kill Zilda.
The Doctor and Leela are sealed into metal bonds with an elaborate molecular code. As the Doctor tries to work out the molecular combination, Uvanov takes the sandminer into a sand storm to find a rich stream of ore.
Poul talks to the Doctor and Leela and admits he doesn't think they're guilty, and wants to know who they think killed the others. The Doctor convinces him to free them and then suggests the robots are responsible. As they go to investigate the cargo bay where Chub died, Zilda slips into Uvanov's quarters and goes through his files. The Doctor figures out that Chub tries to grab a package that was stuck, and must have called for a robot.
As the robot with the corpse marker approaches Uvanov's quarters, Zilda finds a file with something that upsets her, and calls up to the bridge to accuse Uvanov of murder. Toos contacts Poul and sends him to check on Zilda. He leaves them in cabin and the Doctor notes to Leela that if robots can turn against humans, it'll be the end of their civilization.
Poul bursts into Uvanov's quarters to find him standing over Zilda's corpse. Poul confines the Commander to quarters after knocking him out. Leela senses something wrong and the Doctor dismisses her… just as the sandminer's engines jammed, throwing them everywhere. Toos tries to maintain control while Poul goes to find Dask, ordering one of the robots to watch the unconscious Uvanov. The Doctor and Leela go to the bridge and Toos reveals the engines are on overload and she must shut down. Dask calls up to reveal that Borg is dead. The Doctor goes to sabot age the engines but Dask bursts in and the two struggle as the engines race to overload…