Charlie Vaughn, a young Boy Scout, is devastated to learn that his family can't afford to bring Charlie's loyal dog Nixie with them when they emigrate from Earth to a human colony on Venus for his father's new job. Charlie rebels by running away with Nixie, but the police catch him and return them both home. Charlie's father tells him that the only way they can afford to bring Nixie is if they ship him as freight, using a dangerous procedure called sleep-freezing. Nixie would be put to sleep for the duration of the five-month voyage, but there would only be a 50% chance that he would wake up at the end. Charlie agrees to take the chance. Before leaving Earth, Charlie's Boy Scout troop leader makes Nixie an honorary "Tenderfoot Scout", in recognition of the fact that Nixie has accompanied Charlie to all his Boy Scout meetings and hikes. Nixie is sleep-frozen, and Charlie's family boards the spaceship for the long voyage in tight quarters. When they finally arrive on Venus, Nixie is successfully revived, much to Charlie's delight. The family settles in a colony called Borealis, on Venus' north pole. Venus is hot, rainy, and densely populated by dangerous jungle. Charlie joins a new Boy Scout troop, and Nixie is also accepted as a Tenderfoot Scout. Charlie befriends a boy named Hans Kuppenheimer, a skilled navigator who was born on Venus. Although Hans has never seen a dog before, he forms a strong bond with Nixie. Troop leader Mr. Qu'an takes the Scouts on an expedition through the jungle. Because Borealis is on the north pole and the sun never sets, Charlie can't use a compass or the sky to navigate. Mr. Qu'an teaches Charlie a new navigational system using special instruments, but it is difficult to master. Hans also teaches Charlie to watch out for screwbugs that burrow into your arm and giant fireflies that can paralyze their victims. After the expedition, Hans brings Charlie to his house, on a plantation outside of town. Hans wants to show Charlie around the dense jungle near the plantation, and he insists on leaving his navigational instruments at home, since the land is so familiar to him. He leads Charlie and Nixie through a leech-infested stream and thick vegetation that is difficult to traverse. They arrive at a waterfall, where Hans is stung by a giant firefly that paralyzes him and makes him pass out. Unable to navigate the land, Charlie struggles to retrace their steps and carry Hans' unconscious body through the jungle. Charlie gets lost and seriously injures his leg. Unable to walk, Charlie orders Nixie to fetch Hans' father, hoping that the dog will understand the command. Nixie leaves and Charlie passes out. Nixie arrives at the Kuppenheimer house, where Mrs. Kuppenheimer is disturbed to see him alone and full of leeches. Sensing that something is wrong, she sends for her husband. Some time after Nixie saves the boys' lives, the dog is given a life-saving medal by the Borealis Court of Honor.