Part OneSeries Episode Number: 603
World Premiere: Thu 5 Jan 1984 - 6:41pm GMT [BBC One] (United Kingdom)
First Broadcast: Fri 7 Dec 1984 - 11:00pm CST [WTTW 11 Chicago]
Running Time: 24 minutes 48 seconds
7.60 Million (UK)Appreciation Index: 65 (UK)
Chart Position: 51 () (UK)
Seabase 4 is on alert as a strange craft approaches. But the crew has been infiltrated by the enemy, so Commander Vorshak's solutions are scuppered at every turn.