The Doctor gets through the door of Kellman's quarters and hears Sarah's screams. Using gold dust, the Doctor destroys the silver slug-creature, which he identifies as a Cybermat. Sarah collapses, her veins glowing, and the Doctor places her into the transmit beam in the hopes it will clear the poison from its system. He sends Harry with her but the transmit system doesn't work – its pentalium drive is missing and the Doctor concludes Kellman is responsible. Kellman, listening in, hides his spy equipment, grabs a neck chain with the pentalium drive on it. then grabs a gun and barricades himself into the room.
The Doctor improvises a replacement for the pentalium drive while Stevenson and Lester go after Kellman. On Voga, the leader Vorus monitors a giant missile on the planet then tells Magrik they only have four hours until the Cybermen arrive as per Kellman's report. He orders that the missile be equipped with a bomb within the next four hours.
Stevenson and Lester get Kellman's door open but he's nowhere to be seen. The Doctor manages to activate the transmat and Harry and Sarah Jane arrive on Voga. The transmat has filtered out the poison and Sarah Jane makes a rapid recovery. Harry wanders off to examine the gold when the Vogan guards arrive and take them prisoner.
Stevenson finds Kellman and they get into a Mexican standoff and Kellman volunteers to be locked in his quarters, but Lester grabs him from behind. The Doctor confronts him and notes that the Cybermen can be destroyed by gold, which coats their breathing apparatus. He concludes that Kellman is stalling for some reason.
The Cybermen have detected the energy transmission from the transmat and prepare to invade Nerva. On Voga, Vorus confronts Harry and Sarah Jane and reveals that the plan was that only four humans would survive the plague, but they're not among the number they left to survive. Before they can answer his questions, Vorus' superior Tyrum calls and Vorus has them taken off.
Kellman is unimpressed by Stevenson's threats and demands for the pentalium drive. The Doctor manages to activate another cybermat which he directs toward Kellman. Kellman breaks and shows them the pentalium drive. Harry and Sarah Jane have been chained up but they start to work on their soft gold chains.
Vorus goes to Tyrum who knows about the new humans. Tyrum prefers to hide from the Cybermen and the universe at all, and plans to take control of the minds. A furious Vorus storms out to muster his supporters against Tyrum's forces. He has Magrik send a detachment to kill Harry and Sarah Jane so they can't incriminate him. The Doctor reactivates the transmat but can't beam anyone up. They detect the approaching craft which doesn't give any response.
Harry and Sarah Jane free themselves and hide as Vorus' men arrive. They're quickly spotted and flee. The Cybership approaches Nerve despite Stevenson's warning of quarantine. Harry and Sarah Jane are finally cornered but Tyrum's militia show up and take everyone prisoner.
The Cybermen dock and the Doctor lead Stevenson and Lester to the airlock to try to stop them entering. The Doctor fails to seal the airlock and the Cybermen come in. Stevenson and Lester open fire without affect but the Cybermen blast them down. The Doctor tries to sneak off and is quickly shot down as well.