Dalek weapons are useless due to the power drain so they make a truce with the Doctor.
The energy drain has disabled the Daleks’ energy-based weaponry, much to the Doctor’s glee. They are also seeking parrinium; their own worlds are falling victim to the plague – or so they say. What they don’t say is that there are several more Daleks hidden on their ship. The Doctor, the Marines and the Daleks are forced into an uneasy alliance to find the source of the energy drain so they can escape. However, they are all captured by the Exxilons in a skirmish that ends with the death of Captain Railton and one of the Daleks. The Doctor saves Sarah from sacrifice, but is recaptured and is himself sentenced to die for assault on the High Priest.
Back at their ship, the remaining Daleks replace their electronic weaponry with mechanical projectile weapons and quickly master the Exxilons. In the confusion, the Doctor and Sarah flee down a nearby tunnel. The Daleks then “negotiate” a deal with the High Priest, which forces the natives to mine the parrinium. In return, members of the Space Corps are in charge of wiping out a renegade group of Exxilons. The deal also states the Doctor and Sarah will be returned to the Exxilons – dead or alive. Peter and Jill protest, but Galloway (who has taken charge despite the last wishes of expedition commander Stewart) insists it’s the only way if they want the parrinium.
In the tunnel, Sarah realizes that the sacrificial ritual had been meant to end with them being sent down the tunnel – something in here was meant to complete the sacrifice! Both realize that this is probably the source of the strange roars they hear echoing in the tunnel. She also wonders how the Daleks were able to move if they were robots (and thus electronic); the Doctor explains that Daleks move by psychokinetic power (and are thus unaffected by the power drain). At a junction the Doctor has Sarah wait whilst he has a look down the other tunnels for a way out. While she waits she is frightened by the appearance of another Exxilon.
In the new tunnel, the Doctor is about to head back when an enormous, metallic, snake-like creature rears up to strike at him.