An inventor named Allie Fox drives with his son, Charlie, through a billboard-laden strip of town, complaining that Americans are bombarded with advertising, and the country has become “a toilet.” They stop at a hardware store for supplies, but Allie rejects the product he requested because it was manufactured in Japan. Instead, he and Charlie find the same item at the dump. In the days ahead, Allie become restless and believes the United States will soon be at war. Their farmer landlord, Mr. Polski, is angry when Allie arrives late with an invention called “Fat Boy.” Allie demonstrates how the machine is able to turn a glass of water to ice. Although Allie claims he can build a larger model that will keep the farmer’s asparagus crop from spoiling, Mr. Polski is unimpressed. After the rejection, Allie becomes obsessive about relocating to the jungle. Allie has Charlie deliver a letter to Polski, announcing his desire to leave the country and go to the Mosquito Coast. Polski tells Charlie that his father is a dangerous man who is going to get his family killed. Allie is joined by his sons Charlie and Jerry, twin daughters, April and Clover, and wife, Mother, for the long trip. During the journey, Allie expresses his disdain for religion to Reverend Spellgood and his wife. Emily Spellgood, the minister’s daughter, strikes up a conversation with Charlie as he surveys the ocean with his binoculars. She asks about his father’s profession, and does not know whether to believe Charlie’s claim that his father is a “genius.” However she offers to become his girl friend. At night, Mother Fox watches the twins at a local hotel, while in a bar, Allie strikes a deal with a local real estate agent. When Allie returns, he announces to his wife that he has purchased a town called “Jeronimo.” The next day, boat captain Mr. Haddy transports the Fox family to an isolated tropical jungle island. When the boat docks, Allie runs ahead and discovers the town to be barely habitable. He announces to his family that they will build a spacious compound. April and Clover miss their home, but Allie explains that they left because he did not want the family to witness the decline of the United States. The next day, Allie assembles local residents to plant crops, build shelters, and start a fish farm. Meanwhile, Allie builds contraptions to catch rainwater and wash laundry. Mr. Haddy brings bolts of cloth from which Mother makes shirts, rompers and shorts. Allie is convinced that his children are learning important survival skills. Word spreads of Allie’s accomplishments, and Rev. Spellgood visits to see for himself. Allie does not like the idea of the clergyman proselytizing on his estate, and suggests that workers who want to attend church services go back to the mainland. When the compound is finally built, the Fox family celebrates with the workers. Later, Allie builds a larger version of Fat Boy, which will provide air conditioning for the compound. The invention also produces blocks of ice that Allie provides to the natives for free. He soon grows restless and wants to share his ice with a nearby indigenous tribe that is isolated from civilization. When Allie reaches the tribe, he unwraps the gift to find that the ice has melted away. One English-speaking native tells Allie and his group to go away. While Allie confers with a fellow white man, Charlie explains to the tribe why they brought the ice and what makes it special. When Allie and his group leave, he explains that the tribe is holding three white men prisoner. They have a plan to escape, and Allie offers them refuge in Jeronimo. The next day, worker Francis Lungley is picking tomatoes in the hot house, and comes upon three strangers with rifles. He alerts Allie, who soon discovers that the three prisoners are actually mercenaries. Allie offers them a boat and a chance to leave. However, they like the paradise Allie has created. He tells them that the compound is undergoing an ant invasion, but they insist on staying. The mercenaries make themselves comfortable in a section of the house until Allie dismantles it with a chainsaw, claiming it is the only way to get rid of the ants. However, the mercenaries are undeterred, and Allie gives them lodging in the bunkhouse. Late at night, per his father’s instructions, Charlie climbs to the top of the giant Fat Boy and bolts the mercenaries in their quarters, inside the icemaker. As Allie starts the machine, the men attempt to shoot their way out, causing an explosion that spreads fire throughout the compound. In the morning, Allie stares numbly at the destruction, although he tells Mother the fire has freed him. The family wants to return to America but Allie insists there is nothing left for them back home. America has been destroyed by nuclear war. Allie builds a houseboat by the ocean, a latrine and a vegetable garden. One day, Mr. Haddy brings turtle meat and other food, and warns that the rainy season is coming. If Allie does not move his camp, it will wash into the sea. Sometime later, Mr. Haddy gives Charlie parts of an outboard motor to hide. He says the family will need it to escape when the rains come. Allie awakens and discovers a pounding storm outside. The family gathers in the houseboat as it is swept out to sea. As Charlie hands his father the motor parts, Allie insists on traveling upstream rather than toward Mr. Haddy’s town. By morning, the storm passes, and the family floats on the river. After the motor quits, Allie announces the rudder is missing. He ties a rope to his ankle and dives overboard. After an uncomfortable length of time, Mother pulls the rope aboard but Allie is gone. Mother becomes hysterical, and her sons suggest they find Mr. Haddy. Suddenly, Allie climbs aboard with the missing part, and calls them traitors. As punishment, Allie tows his sons in a skiff behind the boat. Mother wants her sons back on board, but Allie refuses. Soon, the family hears a church choir, and Rev. Spellgood’s booming voice at his compound. Abruptly, Allie docks his craft and goes to the church to confront the minister. Instead, he finds parishioners listening to the sermon on a widescreen television, and the Fox family returns to their boat. That night, Charlie and Jerry return to the preacher’s house, and Emily Spellgood gives them keys to a jeep. Charlie and Jerry want their mother and sisters to join them, but Mother refuses to leave her husband behind. Suddenly, they see the church bell tower on fire. Mother orders Charlie to round up the twins. When Mother and the boys inform Allie they are leaving, he calls out to them, but the Rev. Spellgood shoots Allie in the chest. The family carries him to the boat. As Charlie and Jerry paddle, Allie wants to know if they are traveling up river, then dies. The Fox family returns to their life in America. Allie runs ahead and sees the town is dilapidated and barely habitable. He announces to his family that they will build a spacious compound from scratch. When April and Clover miss their home, Allie explains that they left because he did not want the family to stay and watch the decline of America. The next day, Allie assembles locals to plant crops. For several weeks, every waking hour is spent building shelter. Allie assigns one worker to start a fish farm. Meanwhile, Allie builds contraptions to catch rainwater, and wash laundry. Mr. Haddy brings bolts of cloth that Mother sews into shirts, rompers and shorts. Allie is convinced that his children are learning important survival skills. Soon, word spreads of Allie’s accomplishments, and the Rev. Spellgood visits to see for himself. Allie does not like the idea of the clergyman proselytizing on his land, and suggests that workers who want to attend church services go back to the mainland. After Rev. Spellgood quotes from Exodus 5, Allie demands that he leave. When the compound is finally built, the Fox family celebrates with the workers. Later, Allie builds a bigger version of Fat Boy. When it is finished, he demonstrates how the machine manufactures snow, and can provide air conditioning for the compound. The invention also produces blocks of ice that Allie provides to the locals for free. However, he grows restless and wants to share his ice with a nearby indigenous tribe isolated from civilization. Along the journey, Jerry Fox complains that there is nowhere to sleep. Hi father demands he stop whining. In the morning, Allie meets up with the tribe, but when he unwraps the gift, the ice has melted away. One native speaks in English and tells Allie and his group to go away. In the distance, Allie sees a white man, and speaks with him as Charlie explains to the tribe why they brought the ice and what makes it special. When Allie and his group leave, he explains that the tribe is holding three white men prisoner. He offered to help them escape, but they claim to have a plan, and he suggested they follow his trail to Jeronimo. The next day, worker Francis Lungley, is picking tomatoes in the hot house, and comes upon three strangers with rifles. He alerts Allie, who soon discovers that the three prisoners he invited to Jeronimo are actually mercenaries. Allie offers them a boat and a chance to leave. However, they like the paradise Allie has created, and are not eager to go. Allie tells them that the compound is undergoing an ant invasion, but they decide to stick around anyway. The mercenaries make themselves comfortable in a section of the house until Allie takes it apart with a chainsaw claiming it is the only way to get rid of the ants. However, the mercenaries are undeterred, and Allie puts them up in the bunkhouse. Late at night, per his father’s instructions, Charlie climbs to the top of the giant Fat Boy and bolts the mercenaries in their quarters, inside the icemaker. As Allie starts the machine, the men try shooting their way out. It sets off a giant explosion that destroys the machine, and spreads fire throughout the compound. In the morning, Allie stares numbly at the destruction, although he tells Mother the fire has freed him. The family wants to return to America but Allie insists there is nothing left for them back home. America has been destroyed by nuclear war. Allie gets to work and builds a houseboat by the ocean, a latrine and a vegetable garden. One day, Mr. Haddy brings turtle meat and other food, and warns that the rainy season is coming. If Allie does not move camp, it will wash into the sea. Sometime later, Mr. Haddy gives Charlie parts of an outboard motor to hide. He says the family will need it to escape when the rains come. Allie awakens and discovers a pounding storm outside. The family gathers in the houseboat as it is swept out to sea. As Charlie hands his father the motor parts, Allie insists on traveling upstream instead of toward Mr. Haddy’s town. By morning, the storm passes, and the family floats on the river. Soon, the motor quits. Allie announces the rudder is missing. He ties a rope to his ankle and dives overboard. After an uncomfortable length of time, Mother pulls the rope aboard but Allie is gone. Mother becomes hysterical, and her sons suggest they find Mr. Haddy. Suddenly, Allie climbs aboard with the missing part, and calls them traitors. As punishment, Allie tows his sons in a skiff behind the boat. Mother wants her sons back on board, but Allie refuses. Soon, the family hears a church choir, and Rev. Spellgood’s booming voice at his compound. Abruptly, Allie docks his craft and makes his way to the church to confront the minister. Instead, he finds parishioners listening to the sermon on a widescreen television, and the Fox family returns to their boat. At night, Charlie and Jerry return to the preacher’s house, and persuade Emily Spellgood to help them. She gives them keys to a Jeep. Charlie and Jerry want their mother and sisters to join them, but Mother refuses to leave her husband behind. Suddenly, they see the church bell tower on fire. Mother orders Charlie to round up the twins. When Mother and the boys inform Allie they are leaving, he calls out to them, but the Rev. Spellgood shoots Allie in the chest. The family carries him to the boat. As Charlie and Jerry paddle, Allie is paralyzed but wants to know if they are traveling up river, then dies. The Fox family returns to their life in America.