Orville, a bumbling orphanage groundskeeper, runs away from the local sheriff after crashing a toy plane through the post office window. After hiding in the back of a truck, he is dropped off at a secret spaceship development agency. There, handyman Lester discovers Orville staring at the rocket and delivers him to the office of head scientist Dr. Wilson. Wilson's secretary, Janie, confuses Orville for visiting aeronautics professor Dr. Orvilla and invites him to wait for his meeting with Wilson. As soon as Orvilla arrives, the two men fight over who is the real scientist, and Wilson, who easily discerns Orville's low I.Q., kindly suggests that Lester keep an eye on him until the rocket, which is set to travel to Mars, is launched. While Janie worries about Wilson's safety during the trip, Lester and Orville load supplies onto the spaceship. After a series of mishaps, they finally finish, and Wilson joins them on board to check the controls. The moment he disembarks to greet his crew, however, Orville plays with the control panel and accidentally launches the ship. A horrified Wilson races to the engineering room, where he follows the ship's progress on a video screen. Lester, desperately fiddling with the steering, flies the spaceship under the Brooklyn Bridge and through the Lincoln Tunnel. The government assumes aliens have invaded and orders the ship shot down, and when Lester hears this on the radio, he routes the rocket into space. Meanwhile, Wilson, fearing that he will look silly, refuses to reveal the truth to the government, and his assistant opines that the situation will force citizens to realize that the country needs a better air defense system. Soon, Lester and Orville touch down in New Orleans during Mardi Gras. Assuming they are on Mars, they don their space suits and are quickly frightened by a group of masked and costumed revelers. At the same time, Mugsy and Harry, escaped convicts who greatly resemble Lester and Orville, stumble across the spaceship and trade their prison uniforms for space suits. While Orville and Lester search for the Martian leader, Mugsy and Harry use Wilson's laser guns to rob the state bank and steal new clothes. When news spreads that two men dressed as astronauts have robbed the bank, Lester and Orville are forced to flee the city. They make it back to the ship, only to be hijacked by Mugsy and Harry. At Mugsy's command, they take off for Mars, not realizing that they are headed for Venus. When they touch down, the veil of smoke outside the window prompts Orville to wonder if they have landed in Los Angeles. Venus is run by a race of gorgeous women whose queen, Allura, banished all men 400 years before after discovering her king kissing a handmaiden. While exploring the planet, Orville is chased by a gigantic lapdog and stumbles onto a glen filled with bathing beauties. The women, who are eager to see men once again, capture him and bring him to Allura. Although she trusts no men, her subjects convince her to name Orville king. Soon after, Lester, Mugsy and Harry are also brought before the court, where Orville orders Lester saved and the other two imprisoned. On the way to the jail, however, Mugsy charms the guards and persuades them to stage a revolution. At court, Allura gives Orville extra-sensory perception balloons that will break every time he thinks about another woman, and within minutes, all three have popped. Disgusted, she orders him and Lester arrested, but just then, Mugsy and Harry arrive surrounded by soldiers who demand their right to a democratic vote. The women elect to save the men, until Allura shows them images of the Adonis-like men who used to live among them, after which the four mugs are voted off the planet and deposited in their spaceship. The rocket heads straight to Earth, and when it lands, the men are hailed as heroes. During the parade in their honor, Allura sends a greeting to Orville, in the form of a cosmic egg in the face.