Part FourSeries Episode Number: 483
World Premiere: Sat 23 Sep 1978 - 6:21pm BST [BBC One] (United Kingdom)
First Broadcast: Fri 1 Dec 2000 - 10:30pm CST [Prairie Public Television]
Running Time: 24 minutes 50 seconds
8.20 Million (UK)Appreciation Index: 67 (UK)
Chart Position: 36 () (UK)
Pursued into the catacombs by the Graff and attacked by the ferocious Shrivenzale, the Doctor and Romana struggle to stay alive and find the first segment of the Key to Time.