The movie opens with title and credits shown over watercolor paintings, consisting mostly of red, brown and black, of an other-worldly landscape (painting of John Cline). A narrator tells us, "The year 1990, the problem of traveling to the moon has been solved for many years. Space stations have been built there and authorized personnel come and go as they wish, but the moon is a dead world. And the great question about space still remains, does life exist on another planet? To seek an answer to this question, the major powers of the world have been actively preparing at the International Institute of Space Technology to explore the planets Venus and Mars." Allan Brenner (John Saxon) enters the Astro Communications office to see Laura James (Judi Meredith) for a lunch date. She has been monitoring signals believed to be from another planet in our galaxy.On an alien world, we see their sun set over a beach. Their counterparts to ours on Earth are sending signals out into space. Their technology is equal to, or greater than our own. Allan and Laura finish their lunch outside as Paul Grant (Dennis Hopper) on the left and Tony Barrata (Don Eitner) on the right join them at their table. They barely start their lunch when an announcement is made calling all personnel to assemble for an important message from Dr. Farraday (Basil Rathbone). The four are joined on their walk to the assembly by Cmdr. Anders Brockman (Robert Boon). Farraday tells the assembled that they have deciphered the message send by another civilization in space. An ambassador will be dispatched to Earth from their planet. On the alien planet a ship is prepared and launched. It is a spherical shaped craft with a belt of two metal tubes near the bottom. The aliens are human-like in their appearance. An alien probe is sent to Earth prior to the main ship's arrival and lands in the ocean. The capsule is retrieved and sent to the IIST labs for study. A record of the alien ship's entire flight is included in the probe. Farraday and his assistant (Forrest J. Ackerman) enter the Communications office and confer with Laura. Laura plays the alien transmission of their flight, including the crash landing on Mars. Farraday believes there may be survivors on the alien ship. Farraday calls a press conference for the next morning.Farraday proposes a rescue mission using the spaceship, Oceano, and to push up the schedule six months. Supply ships are sent to the moon. Farraday and his staff have moved to the moon to supervise the rescue mission. Laura is unhappy that Allan Brenner will not be on the Oceano rescue ship with her. The rescue ship is launched and Allan watches it depart in his spacesuit from the surface of the moon. Brockman reports a successful launch to Farraday. Brockman reads a book, as Paul Grant and Laura James get their meal. Before they can eat the ship encounters a sunburst that damages some of the ship's instruments. Laura contacts Farraday and reports that they have entered the orbit of Mars using emergency instruments. They begin their search for the alien's ship. They find it and report same to Farraday. The Oceano lands on Mars not far from the alien ship. Brockman and Grant don their space suits and walk over to the alien ship. Brockman enters the disabled alien craft only to discover the crew dead. Back on Earth, a newspaper headline announces, "Successful Landing on Mars; Alien Spaceship Discovered." Another article is titled, "Single Dead Astronaut Found on Spacecraft; Mystery Deepens." On the Moon base, Brenner and Tony Barrata propose taking the smaller rocket, Meteor, to Mars and deploying the search satellites immediately. Farraday explains that the Meteor can only carry a small amount of fuel, not enough to land on Mars, let alone return to Earth. Brenner explains they will land on Phobos, and then take the rescue ship to the surface and return on the Oceano. Farraday agrees to consider the plan. He finally agrees and the Meteor arrives in orbit around Mars. The satellite is deployed and the Meteor lands on the tiny moon, Phobos. Brockman calculates that the Meteor must depart within thirty minutes or they will be stuck on the tiny moon for a week. As luck would have it, the Meteor landed close to the other alien ship, the rescue ship, the one thought to have landed somewhere else on Mars. Brenner and Barrata walk to the rescue ship. They find the sole occupant, a woman in a spacesuit and carry her back to the Meteor. The Alien Queen (Florence Marly) is placed in a seat while Brenner and Barrata decide who will remain behind, as the craft can only carry two. Brenner crash lands on Mars and carries the Queen back to the Ocean. Brockman and Grant go out to find Brenner and the Queen, now lost in a sandstorm. The storm passes and Grant enters the Oceano carrying the Queen. She is wearing a red spacesuit that is quite form fitting. We can see her skin is a greenish color, but otherwise she is quite human in appearance. Laura asks, "Paul, who brought her?" Before Grant can answer, the door opens and Allan Brenner walks in. Brockman explains there is not enough fuel to stop on Phobos to retrieve Tony Barrata. He conveys his concern to Farraday who assures Brockman that a rescue ship will be dispatched to rescue Barrata, but Tony will need to conserve his emergency rations.The Alien Queen begins to come to. The first person she sees is Paul Grant. She smiles at Paul, next at Cmdr. Brockman and finally at Allan. She registers her approval with a toothy grin. But when Laura steps up there is a marked change in her countenance. The crew takes note of this. Brockman assigns the task of seeing to the passenger to Paul Grant. "I thought of suggesting it to Laura, but it seems our visitor doesn't get along very well with her own sex." The Oceano departs Mars and the crew goes about their duties. Paul is showing the Alien Queen how to drink water from a bottle. We now get a good look at the so called ambassador. She is very human-like in her appearance, except for the greenish cast to her skin. Her hair is white, cut short, lacquered, and pulled to a point near the back of her head. She drinks the water, but refuses solid food. It is clear Paul is enjoying his duty. Brockman wants to study her blood. He thinks it may be high in chlorophyll. When Laura gives him a syringe, and the Queen sees the needle, she recoils in horror. She knocks it to the cabin floor, breaking it. Brockman observes, "This is more than some childish fear of the needle. Perhaps she has an extremely low pain threshold. Perhaps...But we mustn't do anything that may affect her health adversely. She is probably the most valuable specimen for scientific research in the history of our planet. To get her back to Earth safely has to be our first consideration." The sleep period buzzer sounds and Paul is assigned the first watch. Paul records his notes on tape. He hears a strange buzzing sound, like a hive of bees. He walks back to investigate. The Queen places her hand on his shoulder. When he turns to look at her, she is smiling, but her eyes have lit up. Paul is mesmerized and she approaches him.The next morning, Brockman enters the cabin and sees Paul. He thinks Paul is asleep. He tries to wake the crewman, but Paul slumps over in his chair. Brockman calls to Laura and Allan to help. Brockman pronounces Paul dead. Laura goes back to check on the passenger. An examination of Paul's wrist shows a wound and a lot of blood. Laura's scream brings her crew mates back to the passenger. The Queen is asleep; her mouth shows a trickled of blood on the corner. Brockman says, "Now we know how she feeds at least." "She's a monster," Allan replies. Allan wants to destroy the passenger, but Brockman disagrees and explains he will feed her with blood plasma. Laura reports the findings to Farraday. Paul Grant's body is disposed of in space. Allan is troubled by the fact that there was no sign of a struggle. Brockman speculates that some anesthesia in her saliva allowed her to feed with no resistance by Paul. Brockman and Laura give her the first taste of blood plasma. Brockman records his notes on tape. He concludes that the plasma seems to satisfy her hunger for blood, but adds that they ran out of plasma and will need to provide blood donations from the remaining crew. He stops and notices the alien in her room and the strange buzzing sound from the same location. She approaches the commander. He pulls a gun and points it at her. He drops the gun and stares into her eyes.The next day, with Brockman dead, there is no one to countermand Allan's action to immobilize the alien vampire. He ties her to a chair and tells the unconscious creature, "When you wake up this time you won't be able to move." Allan is now convinced she must have hypnotized her prey before killing and consuming their blood. Farraday wants Brockman's body returned for autopsy. During the next sleep cycle, Laura sleeps while Allan remains awake and reads a book. The Queen awakes and using some power, burns the ropes securing her arms to the chair. She walks past a sleeping Laura and heads towards Allan. Laura awakes in a start and gets up. She notices the ropes and the empty chair, but only slowly walks to the control room. There she spots the alien crouched over Allan, feeding on his blood. The two scuffle and in the process, Laura scratches the alien's back. When the Queen notices her own green blood on her hand, she runs away shrieking. Allan is on the floor and regains consciousness as Laura treats the wound on his wrist. He asks, "She got to me didn't she?" Laura explains that they fought and she ran away. The pair go to check on their visitor. The alien is laying on a bed with one arm brushing the cabin floor. A puddle of green fluid is below her outstretched arm. Allan observes that she is dead and why she wouldn't allow the blood sample; she's a hemophiliac. She bled to death.The Oceano approaches and lands on Earth. When Laura opens a cabinet to retrieve goggles she discovers that it is filled with red pulsating eggs sitting in a green gel. All the pieces come together for Allan. He concludes, "That's it. That's why they sent her. She wasn't just an ambassador, she was a Queen. A Queen Bee. Maybe this is how their society is set up. A Queen who does all the breeding. Or maybe their planet was dying and they just sent her to bring her kind to Earth. Laura, we have to destroy these." Laura reminds Allan that it is up to the scientific community to study and control this remarkable find. Laura notices more eggs when she opens another cabinet. Farraday enters with his staff and they retrieve the eggs. We close with a close-up of the red, pulsating eggs on a tray, followed by the cast credits.
Output: Question: How do the astronauts keep the alien alive?, Answer: to drink water