Episode 1
Series Episode Number: 265World Premiere: Sat 21 Mar 1970 - 5:16pm BST [BBC One] (United Kingdom)
First Broadcast: Tue 7 Apr 1998 - 7:30am EDT [CTV Sci-Fi Channel]
Running Time: 24 minutes 33 seconds
7.10 Million (UK)
Appreciation Index: 60 (UK)Chart Position: 60 () (UK)
Recorded on Fri 13 Feb 1970 in Television Centre 3
Archive State: PAL 2 VT
Contact has been lost with Mars Probe 7. When contact is also lost with the recovery ship, UNIT is called in and the Doctor learns that someone is sending messages to the vessel.