Major Jim "Lance" Lansing (Forrest Tucker), an American ex-pilot of the U.S. Air Corps, returns to Scotland after the war and finds much trouble in the glen where he settles because of the high-handed activites of the local laird, Sanin Mengues (Orson Welles), a wealthy South American who, with his daughter Marilla (Margaret Lockwood), has returned to the land of his forefathers. Led by Lansing, the people eventually prevail upon Mengues to restore peace to the glen, but not before a brutish fight between Lansing and Parlan (Victor McLaglen), the Mengues foreman.

After moving from South America to the Scottish Highlands, millionaire Sanin Cejadory Mengues reassumes the title of Laird of Glen Eachen, which he inherited from his grandfather, Sandy Menzies. Obstinate in nature, Mengues soon finds the climate inhospitable, and the language and customs of the Highland people exasperating. While fishing on the loch with his equally stubborn, distantly related cousin Angus, who works as a "ghillie" or fishing and hunting guide for the estate, Mengues begins a quarrel over a large trout, and the confrontation escalates from Gaelic epithets and an overturned boat to Mengues firing Angus. When the locals then refuse to work for him and his cattle roam unmanaged over the glen, Mengues, advised by Nollie Dukes, his factor from Glasgow whom the villagers distrust, closes a heavily used road that leads through his property. By the time American widower, Maj. Jim "Lance" Lansing, a former Air Force pilot who was stationed in the village during World War II, returns there, the disgruntled villagers are burning the laird in effigy. After a quick drink at the pub, where he befriends tinker and former paratrooper Malcolm MacFarr, Lance reunites with his sister-in-law, Kate Carnoch, her husband Luke, and Lance's eleven-year-old daughter Alsuin, who adores Lance, but is unaware that he is her father. Stricken with polio, the bedridden Alsuin is hard-hit by the closing of the road, which inspires her made-up fairy tales and provides people to call to her as they pass. At her request, Lance, whom Alsuin calls "Sir Lancelot," proceeds to the Mengues estate to talk to the laird about the road. Finding the gate locked, he climbs the fence, but before approaching the castle, detours to the loch and takes a swim. Mengues' feisty daughter Marissa spots him trespassing and steals his trousers while he is in the loch. Later, dressed in the clothes he has left, Lance shows up at the castle and manages to meet Mengues, who will only advise him, as a fellow foreigner, to "leave Scotland." Later, while poaching with Malcolm, Lance secretly observes Marissa catch a seven-pound trout and, before she can show it to her friends, exchanges it for the tiny one he caught. To Alsuin, Lance later admits that he admires Marissa for her sense of humor and spunk, and is sorry to have embarrassed her. Marissa, too, seeks a truce by returning his washed and mended trousers, giving Lance an opportunity to petition for the opening of the road by introducing her to Alsuin. After Dukes shows up to report a missing steer, presumably stolen by the tinkers, Lance accompanies him to the tinker camp with Marissa, then fights Dukes to prevent a search of the wagons. Although Parlan MacFarr, king of the tinkers and Malcolm's father, knows that the young tinker Nurrich stole the beast, he keeps silent to protect his own, but personally punishes Nurrich when the outsiders are not around. In order to ensure peace in the glen, a delegation of men from the village regretfully ask Parlan to move the tinkers away from the village. At the castle, upon learning that the tinkers have agreed to leave, Mengues fumes and wants reimbursement for the animal. Lance tries explaining that the tinkers live by a different, though honorable, code, but Marissa retorts that he is an outsider repeatedly taking sides against her family. Pulling Marissa aside, Luke explains that Lance is part of the village, as Alsuin is his daughter, and that, by preventing the search at the tinker camp, he saved Dukes's life. Outside, confronted by Mengues, village men standing at the front gate explain that Dukes is rumored to have gone to Glasgow to hire thugs to beat up the tinkers, and the tinkers have stolen explosives to protect themselves. Realizing that the villagers are standing guard to protect him, Mengues softens. Lance correctly guesses that Malcolm will set up the explosives on a road from Glasgow at a certain bridge, and he and Marissa park the car on the bridge, knowing Malcolm will not harm them. When the Glasgow men drive up in a lorry, Lance fights Dukes. The tinkers then challenge the thugs to battle, but a gunshot fired from the hill above stops them. Backed up by men from the glen, Mengues orders Dukes and his thugs out of the area. After inviting the tinkers to stay, Mengues apologizes to all by explaining that he has recently learned the difference between a lord and a laird. A lord, he says, takes care of the people and land belonging to him, while a laird belongs to the land and the people. With peace restored, the road re-opens, and during the wedding festivities of Lance and Marissa, Mengues, dressed in a kilt, promises Alsuin, who knows now that Lance is her father, that they both will be dancing within six months. Parlan and Malcolm enjoy the party from the window, until they realize it is an excellent night for poaching.