Ian frantically yankes wires from within until the cpasule malfunctions. The capsule stops and the robomen are made to pull it back. Ian opens the bottom of the capsule and slips out, just evading the Dalek fire.
Barbara and Jenny are brought to the control room. The Dalek Supreme orders the humans to be herded into the lower galleries so that they will all be killed by the bomb. As Barbara spins a fanciful tale for the Daleks, Jenny tries to sabotage the computers but is stopped. Barbara tries to use the computers to order the robomen to rebel but is stopped and taken away.
The Doctor scouts the mine. He orders Susan and David to sabotage an aerial while he and Tyler descend into the mineworkings.
Ian recovers from his fall but has to stay in place to avoid roboman patrols.
The Doctor breaks into the Dalek control centre.
Ian uses timbers to block the capsule shaft. The Daleks send the repaired capsule down and it jams against Ian's barricade.
As the Daleks evacuate, the Doctor and Tyler break in and free Barbara and Jenny. Told of the Daleks' plans, he can only wait until David and Susan destroy the aerial. The Daleks detect the Doctor's actions and send a Dalek back to the control room. The Doctor calmly stands in its way. David and Susan break the aerial and the Dalek overheats.
Barbara goes to roboman control and instructs them to turn on the Daleks. Together with the prisoners, they attack and destroy the remaining Daleks. Ian joins the Doctor and tells him about the jammed bomb. Confident that it will be unable to break the crust, they evacuate. A tremendous explosion rips through the Dalek mineworks, but it fails to break through the Earth's crust. The updraft destroys the remaining Dalek saucers.
With the Daleks finished, the rebels clear the debris from the TARDIS. Life returns to London as the human race sets about rebuilding their shattered civilization.
The Doctor and Susan have an awkward conversation and the Doctor goes into the TARDIS to check on the machine. Barbara and Ian pointedly leave David and Susan alone to talk.
David asks Susan to stay with him — to get married and help rebuild the Earth. She tries to tell him that her grandfather needs her but admits she loves him.
The Doctor, overhearing the conversation, locks the TARDIS doors. He tells Susan that she has grown up and deserves to have a life of her own. He tells her to stay with David and that he will one day return. He tells her to "Just go forward in all your beliefs, and prove to me that I am not mistaken in mine" before taking off.
Susan leaves with David, dropping her TARDIS key onto the ground.