The Doctor and Peri are running down a corridor, chased by N'Tian soldiers who are firing at them. They turn a corner and come to a lift. It works too slowly for them, as they can hear the soldiers approaching. The Doctor spies the entrance to a ventilator shaft, and they hide in there as the soldiers approach. The Doctor and Peri head down the shaft, which empties into a chamber, a distribution node, with three large, wall-sized fans. There are ladders leading to holes in the ceiling. Peri is starting to regret travelling with the Doctor.