A town called Glipforg, located on Planet 51 is a very peaceful town, that has green, snail people living there. The Glipforg community is always on the look out for humans, they think humans are evil zombies. The people of Glipforg don't live up-to-date they are very old-fashioned, mostly everything looks like its from the 1950. Everybody in the community knows one another and is very friendly. One day while Lem, a teenage boy who lives in Glipforg, was having a party thrown to him by his parents, because he just got a new job, but the party got ruined. When a emergency signal went off because a human space ship had been spotted. Inside the spaceship is Chuck, an astronaut from the planet Earth. Chuck has landed on Planet 51 because of a mission from Earth. While Chuck steps out the spaceship he steps on a toy duck and everybody at Lem party stares at him. Chuck who has just realized he is on a alien planet runs and ends up at Lems job the planetarium. The Glipforg is now under strict watch and the Base 9 is telling people to watch out for the human because they might turn into a zombie. Lem finds Chuck at the planetarium and they talk to one another only to find out that they both speak English. Lem finds out that Chuck is not what the town of Glipforg think of humans so he then gets Chuck and takes him back to his house to hid and comes up with a plan to help Chuck escape. Lem and Chuck attend the movie premiere of Humaniacs and they dressed up as fans so no one would recognize them, but the plan doesn't work and Chuck is captured. After Chuck saves the Base 9 general from a fire the everyone realizes that Chuck is not actually a zombie and he was never there to harm Planet 51 they let Chuck go back to Earth.