Sean Thornton, an Irish-American from Pittsburgh, returns to Ireland to reclaim his family's farm in Innisfree. He meets and falls in love with the fiery Mary Kate Danaher, the spinster sister of the bullying, loud-mouthed landowner "Red" Will Danaher. Danaher, angry that Sean outbid him for the land adjacent to his property, initially refuses to sanction the marriage until several town locals, including the parish priest, conspire to trick him into believing that the wealthy Widow Tillane wants to marry him, but only if Mary Kate is no longer living in the house. After learning the truth on Sean and Mary Kate's wedding day, an enraged Will refuses to give his sister her full dowry.
Sean, unschooled in Irish customs, cares nothing about the dowry, but Mary Kate is obsessed with obtaining it, the dowry representing her independence, identity, and pride. Angered and shamed by Sean's refusal to confront her brother and demand what is legally hers, she brands him a coward, and, despite living together, they are estranged as husband and wife. The truth about Sean, however, is known only to one other person in the village, the Church of Ireland minister "Snuffy" Playfair. Sean is a former boxer in the United States, a heavy weight champion known as "Trooper Thorn." After accidentally killing an opponent in the ring, Sean hung up his gloves, vowing never to fight again.
Later, in an attempt to force Sean to confront Red, Mary Kate leaves him and boards a train departing the village, although she continually looks around to see if he is coming after her. Infuriated, Sean arrives and drags her off the train, and, followed by the townspeople, forces her to walk the five miles to Red's farm. Sean demands that Red hand over her dowry. Red finally relents and gives him the cash, but to his horror, Mary Kate and Sean throw it into a furnace, showing that Mary Kate never cared about the money, but only that Sean stand up for his wife. Sean and Will slug it out through the village, stop for a drink, brawl again, then become best friends. Sean regains Mary Kate's love and respect, Red and the Widow Tillane begin courting, and all is well, at least in Innisfree.