The crew of the British-American spaceship Churchill, commanded by Colonel Tom Carlsen (Steve Railsback), discovers a 150-mile-long spaceship hidden in Halley’s Comet. Inside are hundreds of desiccated bat-like creatures and three naked humanoid bodies in suspended animation in glass cases. They and a bat-alien are taken back to Earth, but Mission Control loses contact with Churchill and a rescue mission is sent.

Churchill has been gutted by fire, the crew is dead, and the escape pod is missing, but the cases remain intact with the bodies still inside. They are taken to the European Space Research Centre in London. Before autopsies can take place, the female alien (Mathilda May) wakes and drains the life from a guard. She escapes onto the street and drains other humans, revealing that she can shape-shift. The guard revives, but he too can drain the lifeforce from others. The two male aliens (Chris Jagger and Bill Malin) are apparently killed by grenades while trying to escape.

In Texas, an escape pod from the Churchill is found with Carlsen inside. He is flown to London, where he tells what happened. He says he set fire to the shuttle to save Earth, but under hypnosis he reveals a psychic connection to the female alien. Carlson and SAS Colonel Colin Caine (Peter Firth) trace her to a psychiatric hospital in Yorkshire. They think they have her trapped inside the heavily sedated body of the hospital manager Doctor Armstrong (Patrick Stewart), but they have been deceived.

The male vampires have survived by shapeshifting into the soldiers who shot them, and they are in the process of infecting all of London. On her way back to London, the female escapes from her host and disappears. Martial law is declared as the vampirism spreads and people attack other people on the street. Most of the lifeforce gathered is channelled to the female, who transmits it to the ship in geosynchronous orbit above.

Doctor Fallada (Frank Finlay) impales one of the male vampires with an ancient iron weapon. He thinks the aliens have invaded Earth during previous passages of Halley’s Comet. The weapon is delivered to Caine. Carlsen tracks the female to St. Paul’s Cathedral, where she lies on the altar, transferring her power to the spaceship. She tells Carlsen they are one. Caine kills one of the males, and Carlsen impales himself and the female simultaneously. The energy released blows the dome off of St. Paul’s. They ascend to the comet together.

Director Tobe Hooper did Poltergeist with producer Steven Spielberg and was given a three-picture deal—Lifeforce was the first, and then Invaders from Mars and the Texas Chainsaw Massacre. Lifeforce was written by Dan O’Bannon and Don Jakoby, based on Colin Wilson’s 1976 novel The Space Vampires. Wilson was disappointed in the film. It was badly reviewed and a box-office failure but became—you guessed it—a cult film. It was suspiciously similar to Quatermass and the Pit. John Gielgud was offered a lot of money to appear, but the offer was reduced later, and he turned it down. Reviewers called it hysterical vampire porn and deadly silly, though Gene Siskel thought it a guilty pleasure.

The score was by Michael Kamen and Henry Mancini. Billy Idol was offered a role as a vampire but couldn’t do it. The special effects were by John Dykstra—his fourth movie. Director Tobe Hooper almost lost an ear on the freezing cold English moors. The movie features Patrick Stewart’s first on-screen kiss—with Steve Railsback. The dummies, called the Walking Shrivelled, were later used in The Mummy (1999). Frank Finlay was made a Companion of the British Empire during filming. When the Queen asked him what he was working on, he was too embarrassed to tell her the working title was The Space Vampires. The European version has more violent and erotic images and Henry Mancini’s full score.

Mathilda May was only on screen for seven minutes but almost all of it was in the nude. A thousand actresses refused the role, including Marina Sirtis. There was as much attention paid to her pubic hair as there was to Christopher Reeve’s package in the Superman costume. Editor John Grover said he couldn’t believe how much they got away with. May was completely comfortable being naked on set and never bothered with a robe. That made a lot of people uncomfortable, partly because she was only 18 at the time. For a while, there were a lot of extra carpenters on the set, but then it was closed. Makeup artist Nick Maley said his favorite part was her body makeup, but she hardly needed it as her skin was flawless. She was a ballerina, which allowed her to move in a particularly fluid way, but she spoke only French and had to learn her lines phonetically. Full-sized body models were created for the three vampires in suspended animation, and hers was sold for a great deal of money.