The 40th episode of Gerry Anderson’s space adventure series Space: 1999 airs on British broadcaster ITV, starring Martin Landau, Barbara Bain, and Catherine Schell. David Prowse (Star Wars) guest stars. 
An expanding luminescent cloud appears in the moon’s vicinity, and a mysterious illness sweeps the crew of Moonbase Alpha. The affliction strikes most of the male crewmembers, but not all of them. Commander Koenig is among those rendered helpless, and Tony Verdeschi takes command. Eagle 6, which was on a routine reconaissance mission, returns to the moon without fuel and without a trace of life aboard. But when Verdeschi and a security team board the Eagle, they find a vicious creature that kills everyone it can get its hands on. A mysterious voice contacts Moonbase Alpha and demands that the crew turn off the base’s life support. While this ultimatum is delivered, the creature is rampaging through Alpha’s corridors. As Tony and a surviving security guard try to lead their unwanted visitor into a trap in the base’s vacuum chamber, Dr. Russell falls victim to the debilitating disease. The beast is cutting a deadly path toward Alpha’s life support center to do what the crew is unwilling to do. But can they stop it?
written by Charles Woodgrove
directed by Robert Lynn
music by Derek WadsworthCast: Martin Landau (Commander John Koenig), Barbara Bain (Dr. Helena Russell), Catherine Schell (Maya), Tony Anholt (Tony Verdeschi), Nick Tate (Alan Carter), Zienia Merton (Sandra Benes), Dave Prowse (The Creature), John Hug (Bill Fraser), Albin Pahernik (Space/Kreno Animal)
LogBook entry by Earl Green