At co-ed Camp Sasquatch, director Giddy welcomes new arrivals to the summer session. To satisfy his community service, juvenile delinquent, Armand “Flash” Carducci, is assigned to the camp as a counselor in training (CIT). He grumbles about the place, until he catches the eye of a beautiful female camper named Cheryl. Having grown up in a sheltered environment, Cheryl is anxious about interacting with boys, but immediately makes friends with streetwise Nancy who lends her a stylish outfit. Another camper, Tommy McVee, is handicapped and arrives in a high-speed wheelchair. Among the adults in charge, counselor Jamie looks forward to a romantic rendezvous with buxom colleague Fanny, who oversees the girls’ cabin. Across the lake at Camp Patton, director Colonel “Batjack” Hershey and his closeted-homosexual assistant, Felix Foxglove, have modeled their rustic retreat after a military base with a welcoming sign reading: “where outdoor living molds killers.” Every summer, the two rival camps compete in a boxing match known as “Champ of the Lake.” Aware that Flash has been in a few fights, Giddy asks the young man if he will be a sparring partner for their star boxer, “Boomer,” but Flash is not a team player, and refuses. Flash is assigned to Cabin Six and tells the boys to obey one rule, leave him alone. On the first night, an unidentified flying object (UFO) arrives at Camp Sasquatch and drops off a young extraterrestrial, hoping to earn an “Earth Merit Badge.” In the morning, the Cabin Six boys find the alien, dressed wearing a yellow rain hat and hiding in an outdoor toilet. The boys ask its name, but misunderstand and believe the alien says, “Meathead.” At first, they conceal the extraterrestrial in an abandoned outhouse, but during a thunderstorm Meathead takes refuge with the boys inside the cabin. At the recreation center, Flash sees Cheryl working out with the aerobics class and spars with the dull-witted Boomer to impress her. However, Giddy is more impressed as Flash knocks Boomer to the ground. When Nancy realizes that Cheryl has no knowledge of sex or the male anatomy, she and her cabin mates are determined to show Cheryl a penis by the end of the summer. Meanwhile, Colonel Hershey acquires rights to the lake from Native American Chief Rawhide, and plans to force Camp Sasquatch out of business. The Colonel refuses to negotiate when Giddy says he cannot run the camp without access to the lake. In retaliation, Giddy concocts his own scheme and tells the intolerant Colonel that he intends to sell Camp Sasquatch to a sect of Hare Krishnas. Giddy offers to cancel the deal if the Colonel awards water rights to the winner of this year’s Champ of the Lake. However, if Giddy loses, he must relinquish Camp Sasquatch. The Colonel agrees, but as soon as he is back at his headquarters, he assigns one of his henchmen, Sergeant Paladin, to incapacitate Boomer, while the rest of Sasquatch is occupied at a dance. During the event at the recreation center, Cheryl and Flash have their first conversation while slow dancing. Flash claims he is a nice altar boy when Cheryl asks about his mean reputation. Meanwhile, counselors Jamie and Fanny find a secluded place to have sex, but someone barges in, as usual. In her mission to educate Cheryl, Nancy cajoles Eddie, a counselor in training, to run naked by Cheryl’s bunk in Cabin Ten later that night. However, a mischievous boy overhears the conversation and switches the sign on Cabin Ten and the one on Cabin Nine, which is counselor Fanny’s cabin. As a result, Jamie arrives in Cabin Ten expecting a romantic rendezvous, while Eddie slips into Fanny’s cabin and removes his clothes. Both intruders are immediately ousted. The next morning, Flash finally discovers Meathead’s existence, but the boys in the cabin assure him the kind creature is no trouble. At the recreation room, Flash arrives to find Boomer with a broken arm, and Giddy training to box. Flash convinces Giddy that he will fight in Champ of the Lake. Meanwhile, at Camp Patton, the Colonel keeps his boxer, “Mad Dog,” in a cage and feeds him raw steak. Nancy arranges a romantic tryst between Cheryl and Flash by the lake, but tells Cheryl the meeting will involve looking at the stars, while Flash believes they are going skinny-dipping. Nancy and her friends position themselves in a tree to spy on the couple. However, chaos ensues when Cheryl comes face to face with a bear, Flash is kidnapped in the nude by a “counterinsurgency” squad from Camp Patton, and Jamie and Fanny are again interrupted while fooling around nearby. On Champ of the Lake day, Flash wakes up at Camp Patton dressed in a towel and stumbles into Felix Foxglove’s room, where he finds a closet full of women’s clothing. Meanwhile, a sold-out crowd is gathered at Sasquatch recreation center for the boxing match, as the Colonel introduces “Mad Dog,” and Giddy anxiously waits for Flash to arrive. When the young man enters wearing a dress, the crowd is dumbfounded, but the campers of Sasquatch cheer loudly as Flash asks for boxing gloves. During the first round, Flash struggles against the bigger opponent and is continually thrown out the ring. In the next round, Flash appears defeated, and does not get up off the mat. Sitting in the crowd, Meathead transmits a special energy to the young man, allowing him to rise, fight, and fly above his opponent. The Colonel attempts to eliminate the alien with a grenade, but the handicapped Tommy McVee intervenes, knocking the explosive from the Colonel’s hand. Meathead takes control of the weapon, sending it to chase the Colonel out of the recreation center. Although the alien is distracted from relaying superpowers to the ring, Flash still manages to defeat his exhausted opponent. As Flash raises his arms in victory, Mad Dog pulls down his dress, allowing Cheryl to finally get a glimpse of the male anatomy. Having survived the grenade attack, the wounded Colonel begs Giddy to reconsider their deal, but Giddy only offers his rival a self-improvement workshop. On the last day, Meathead says goodbye to his cabin mates as his parents pick him up in their UFO. Before boarding the bus, Cheryl gives Flash a passionate kiss and invites him to visit her.