Episode 4Series Episode Number: 156
World Premiere: Sat 1 Apr 1967 - 5:50pm BST [BBC One] (United Kingdom)
Running Time: 24 minutes 41 seconds
8.40 Million (UK)Appreciation Index: 49 (UK)
Chart Position: 39 () (UK)
Recorded on Sun 26 Mar 1967 in Lime Grove D
Archive State: Missing
The Doctor and Polly discover that the Macra are using the humans to mine the gas that they need to survive. The Pilot is shown the truth, but the Macra are still in control.