Klieg and Parry puzzle over the mathematics behind operating the power systems of the city. The Doctor gives Klieg the solution but warns him not try it. Klieg takes no notice and activates the machinery. Power begins to hum through the complex. In the revitalising room Victoria is standing inside a large Cyberman-shaped sarcophagus when the power comes on.
Kaftan pulls a lever and the lid slams shut, trapping Victoria.
Viner goes to fetch help. When he has gone, Kaftan pulls more switches but is stopped by the Doctor. The Doctor releases Victoria and takes her and Viner to check on Jamie and Haydon. In the other room Haydon operates a control, the room darkens, and a large hypnotic pattern appears on one wall. He theorises that the room was used by the Cybermen for some kind of weapons testing and gets Jamie to operate the machine once more.