Attempting to recover from intoxication, Paul Foster falls victim to the aliens operating the UFOs and launching brutal attacks on Earth for the purpose of harvesting human organs for their own survival.
While Moonbase responds to a UFO sighting, Colonel Paul Foster arrives at the SHADO Research Centre to take part in a mandatory fitness training programme. Tired and hung-over from an all-night party the evening before, he undergoes a gruelling exercise regime supervised by Dr. Frazer, after which he eagerly volunteers for a bath, until he discovers that it is a sauna bath. Setting the timer, Foster falls asleep, but when he wakes up and tries to leave the sauna, he finds that the door is jammed and the temperature control has been turned up to 130 degrees Fahrenheit. He collapses from the heat and is unable to defend himself when two of the Aliens burst in, drag him from the sauna and beat him senseless. The Aliens then take Foster to their craft, where he is knitted out in an Alien spacesuit and a helmet filled with green oxygenating liquid.
When SHADO discovers a break in communications with the Research Centre, Colonel Alec Freeman is sent to investigate. When he gets there, he finds everyone else dead and Foster missing. Freeman realizes that the Aliens have captured Foster, but SHADO Commander Edward Straker gives orders for the escaping UFO to be destroyed on sight, explaining to Freeman that the Aliens will undoubtedly interrogate Foster to reveal SHADO secrets. However, when the UFO breaks cover, Captain Lew Waterman cannot bring himself to shoot the craft down in Sky One, knowing that Foster is aboard. The UFO leaves Earth on an anti-lunar trajectory, but then apparently damaged, the craft changes course back towards the Moon. The UFO crash-lands just 40 km (25 miles) from Moonbase and explodes, but Foster is thrown clear; Lieutenant Gay Ellis rescues him in a Moonmobile. Back at Moonbase, an attempt is made to remove Foster's Alien helmet and get him back to normal breathing, but as Ellis starts to lift the helmet clear, Foster panics and falls to the floor, choking as he coughs up the liquid...
...whereupon Foster regains consciousness to find himself back in the sauna at the Research Centre. Frazer explains to him that he had passed out for a few minutes, the effect of too much drink and not enough sleep.
- Commander Ed Straker - Ed Bishop
- Colonel Alec Freeman - George Sewell
- Colonel Paul Foster - Michael Billington
- Lieutenant Gay Ellis - Gabrielle Drake
- Lieutenant Nina Barry - Dolores Mantez
- Lieutenant Joan Harrington - Antonia Ellis
- Lieutenant Keith Ford - Keith Alexander
- Captain Lew Waterman - Gary Myers
- Dr. Doug Jackson - Vladek Sheybal
- Lieutenant John Masters - Jon Kelley
- Lieutenant Gordon Maxwell - Jeremy Wilkin
- Lieutenant Ayshea Johnson - Ayshea Brough
- Lieutenant Sylvia Howell - Georgina Moon
- Dr. Frazer - Basil Moss
- Lieutenant Gary North - Mark Hawkins
- SHADO Operative - Maxwell Craig
- Voice of S.I.D. - Mel Oxley
- Sylvia Graham - Quinn O'Hara
- Joe Franklin - David Healy
- Dr. Murray - Peter Burton
- Moonbase Medic - Joseph Morris
- SHADO Operative - Burnell Tucker
- Alien - Gito Santana
- Voice of SHADO Research Centre Tannoy - Keith Alexander