SHADO engages in its first battle with the enemy. Sky One cripples an alien ship which crash-lands in a lake. Straker's team capture its pilot, a strange blue-skinned humanoid - and the grim secret behind the aliens' are revealed.

The body of an Alien, recovered after a UFO attack on Moonbase, reveals some startling new evidence which overturns all SHADO's previous theories about the Aliens. For Interceptor pilot Jim Regan, the news has tragic consequences as he becomes possessed by the mind of an Alien held in the body of a Siamese cat!

A Naval vessel shoots down a UFO in the Atlantic, but the Admiralty rejects further investigation into the incident. Straker suspects a cover up and wants to know why, so Foster courts Admiral Sheringham's secretary, Sarah Bosanquet. What they discover could mean the end of all life on Earth...

A UFO imbues three young people with incredible powers. One blows up a radar station, a second steals fingerprints and tries to get aboard a Skydiver sub, blowing it up. The third, a woman, tries to blow up SHADO HQ but the UFO that is feeding her power has now been destroyed.

After a UFO inexplicably destroys itself less than two miles from Moonbase, a mysterious crystal rock is recovered, and it causes the person in its vicinity to hallucinate. The man on Moonbase who found it thinks Mexican bandits have taken over Moonbase. It gets transferred to Straker's office, and he hallucinates that SHADO is simply a set for a TV series, he is an actor named Mr. Burns, Moonbase can be reached by stepping through two doors from the main control room at SHADO HQ, and "Mr. Straker" is not available. Straker breaks the hallucination by jumping in on the scene while the "character" Gen. Henderson is doing a close-up of the line they were doing when the hallucination began.

Reported missing, presumed dead, after a UFO incident which has left SID disabled, astronaut Craig Collins turns up alive and well. But as an operation to complete repair work on SID is planned, Colonel Lake and Colonel Grey discover that Collins is not the man he used to be...

While picking up Lt. Lake at the airport, Straker and Lake find that time has been frozen except for them. Sawdust hangs in mid-air, Lt. Ellis is frozen mid-word on a viewscreen, and one man is taunting them, apparently working for the aliens.

A mysterious dome is found under the sea, that at first looks like the Moon crashed into the ocean. Inside the dome, they find duplicates of SHADO HQ personnel, using non-alien technology - cassette tape recorders - to imitate SHADO instructions to Moonbase and Skydiver.

A woman awakens from a 10-year coma and begins telling the tale about her encounter with aliens, along with her boyfriend, while they were high on drugs. They toyed with the aliens, and the man apparently falls to his death from a bridge or building. The aliens drag him off. She has an accident and falls into the coma. She can't remember quite everything, but the old boyfriend is back, resuscitated by the aliens, and he drugs her so she tells him where the missing part of a device is. He activates what turns out to be a thermo-chemical bomb that will wipe England off the map when the four chemicals meet in a central chamber.