In 1865 in Kurtal, Switzerland, which is located at the base of the famous Citadel mountain, eighteen-year-old Rudi Matt yearns to follow in his late father’s footsteps and become a mountain guide. Instead, however, his mother and his uncle, mountain guide Franz Lerner, have ordered him to wash dishes at the Monte D’Oro inn, whose owner, Herr Hempel, admires the boy and may eventually leave him the inn. Watching over Rudi in the kitchen is Teo Zurbriggen, his father’s ex-partner, and Hempel’s daughter Lizbeth. One day, Teo is forced to once again cover for Rudi after the boy sneaks out of the kitchen in order to climb a nearby mountain. Atop a peak, he hears a distress call from a crag below and rushes to the site. Rudi’s strength and courage help him rescue the trapped man, whom he immediately recognizes as renowned British mountain climber Capt. John Winter. On their walk back to town, John praises Rudi’s father Josef and reveals that he believes in the dream that resulted in Josef’s death: to climb the unconquered Citadel. Rudi piques John’s interest further when he reveals Teo's assertion that, just before his death, Josef had discovered a path to the summit. In town, Lizbeth waits at the foot of the mountain to inform Rudi that Franz has learned that he went climbing, and her concern rouses the jealousy of her suitor, mountain porter Klaus Wesselhoft. Rudi returns home, where his mother begs him not to pursue his father’s dangerous line of work. Soon after, John visits to ask Franz to lead him on a climb the next day, and suggests that Rudi act as their porter. When Franz reluctantly agrees, Rudi celebrates with Teo and Lizbeth, who then learn that John has bought Rudi a new set of climbing gear. The next day, armed with a good luck medal from Lizbeth, Rudi follows Franz and John on the complex climb. At the first camp, they meet another group of climbers, all of whom join John in a toast to Josef. In the morning, John admits to Franz that he has come for a better view of the Citadel, which he plans to scale. After Franz calls the Citadel “evil” and refuses to discuss a possible route up the mountain, Rudi secretly climbs a precarious face on his own to obtain a better view. A slippery slope causes him to fall, however, and John and Franz risk their safety to rescue him. By the time they return to Kurtal, Rudi’s failure is public knowledge. The next morning, Rudi sees John leave town and assumes his career as a mountaineer is forever ruined. Soon after, he learns that Franz has sold his expensive new hiking gear, but is cheered to discover that Lizbeth has bought the boots and is storing them for him. Teo, noting the boy’s disappointment, vows to teach him to be a great guide, and with Lizbeth, sets out training Rudi to climb with a heavy bag of rocks. After Rudi succeeds in all of the tasks, Teo, who was crippled in the accident that killed Josef, has Rudi guide him up a steep slope, then celebrates the boy’s enhanced talents. Teo counsels Rudi never to work for praise but only to assure the safety of his clients. Along their walk home, Lizbeth convinces him to invite her to the upcoming town festival. Their happiness is dashed, however, by the news that John has visited and left town again while they were gone. That night, Teo and Lizbeth urge Rudi to ask Franz if he can be his porter, but Franz refuses Rudi publicly, humiliating him. At the festival soon after, Rudi sulks and refuses to dance, and to spite him, Lizbeth dances with Klaus. When the townspeople discuss two men sighted on the Citadel, Rudi realizes that John has hired Emil Saxo, a guide from a rival town, to lead him up the mountain. The next day, after Teo uses the town telescope to make out three figures on the mountain, Franz deduces that Rudi has sneaked off to join the expedition and gathers four other men to bring the boy down. Meanwhile, at the lowest camp on the mountain, Rudi convinces John that Franz gave him permission to climb with them, and they set out. A rock slide causes a slight head injury to John, after which John tells Rudi to take a message to Franz asking him to join them. Rudi starts down the mountain but then decides to search alone for the passage his father found. When Emil and John return from a supply trip, they find Franz and the other climbers, including Teo, awaiting them. They are about to search for Rudi, but just then the boy returns, battered but jubilant, with the news that he has found a passageway. Franz insists on bringing Rudi home, but Teo argues that the boy deserves a chance. After John agrees, pointing out that by climbing together the glory of the accomplishment will reside with Kurtal, Franz relents. Emil then refuses to climb with Franz, but finally he, too, consents to accompany them. The next day, the group of four reach the passageway, and although Emil declares it too small, Rudi is able to push his way through to the top and pull the others up. A storm in the distance causes Franz to insist that they rest for the night, during which John develops a fever from his head injury. In the morning, Emil urges Franz to continue to the summit with him, but Franz asserts that he must stay with John. Rudi, upon seeing Emil take off alone, determines to join him and sneaks away. Meanwhile, the town uses the telescope to track the group’s progress on the mountain. Although Frau Matt warns Lizbeth that being the wife of a guide is difficult, the girl declares that she desires only for Rudi to live out his dream. On the mountain, Emil falls, breaking his arm. Gruffly, he instructs Rudi to go on and reach the summit alone, but Rudi insists on staying to help Emil back to camp. At the same time, John and Franz discover that Emil and Rudi are gone, and John convinces Franz to summit with him. When they pass Rudi’s abandoned pack along the way, John carries it with him. While Rudi struggles to lead Emil to safety, barely making it back to the camp before the guide collapses, John and Franz reach the top of the Citadel. In town days later, the foursome receive a hero’s welcome, even from Frau Matt, who hugs her son proudly. After John reveals that he planted Rudi’s flag at the top, Emil and Klaus lead a cheer for the boy. Teo rouses the band to perform a victory song, during which Lizbeth kisses Rudi, in full view of the approving crowd.