Based on a story by Vietnam veteran Paul Staples, the film concerns six American Green Berets, held for 17 years in a Vietnamese POW camp. They are finally released in secret, during a delicate trade-talk session between Vietnam and the United States. Captain Tom Watkins, the ex-prisoners' CO, begins to suspect that government-man Adam Roth, who is in charge of the debriefing, may be pursuing a hidden agenda that will result in the early deaths of Watkins and the five men under his command.\
A war vet finds out that a former prostitute had his baby. Doubting it's his, he gives it away, so she reports him. Twenty years later, she still wants to find her son. She meets a young man and falls in love, but the vet's prison term ends.
After policeman Frank Dooley is framed for theft and loses his job on the force, he joins a security guard agency and teams up with inept former defense lawyer Norman Kane. When the two botch a job guarding a local warehouse, they begin to uncover corruption within the company and their union.
A space shuttle mission investigating Halley's Comet brings back a malevolent race of space vampires who transform most of London's population into zombies. The only survivor of the expedition and British authorities attempt to capture a mysterious but beautiful alien woman who appears responsible.