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...

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.