Part OneSeries Episode Number: 398
World Premiere: Sat 19 Apr 1975 - 5:36pm BST [BBC One] (United Kingdom)
First Broadcast: Wed 19 Mar 1980 - 5:30pm CST [WTTW 11 Chicago]
Running Time: 24 minutes 19 seconds
9.50 Million (UK)Appreciation Index: 57 (UK)
Chart Position: 24 () (UK)
Recorded on Tue 03 Dec 1974 in TC1
The Doctor, Sarah and Harry return to Nerva, but at an earlier point in time. The crew are dying and blame a space plague, but the Doctor suspects a survivor may be responsible.