Part TwoSeries Episode Number: 577
World Premiere: Tue 23 Mar 1982 - 7:05pm GMT [BBC One: Not Wales] (United Kingdom)
First Broadcast: Tue 21 Apr 2015 - 8:30pm EDT [Retro TV]
Running Time: 23 minutes 58 seconds
8.50 Million (UK)
Chart Position: 48 () (UK)
After an encounter with the Plasmatons, Nyssa is possessed by strange aliens while the Doctor, joined by Professor Hayter, investigates Kalid's inner sanctum.