Part Four
Series Episode Number: 549World Premiere: Sat 21 Feb 1981 - 5:12pm GMT [BBC One] (United Kingdom)
Running Time: 25 minutes 11 seconds
6.10 Million (UK)
Appreciation Index: 63 (UK)Chart Position: 103 () (UK)
Recorded on Fri 21 Nov 1980 in Television Centre 8
Melkur has become the new Keeper of Traken and begins to access the source manipulator. As the Doctor takes steps to stop him, he discovers the frightening truth about his enemy.