Tipperary, 1848. The inhabitants of Kilthubber village are happily going about their business. Mat “The Thrasher” Donovan, a stalwart peasant, sings as he ploughs the fields. In Knocknagow, a nearby hamlet, lives a family of prosperous tenant farmers: Maurice Kearney, his wife, and their three daughters. While visiting the seaside town of Tramore, Kearney’s daughter Mary meets Arthur O’Connor, a theology student. Father Carroll, a family friend, explains to Mrs. O’Connor that her son, whom she wishes to become a priest, has fallen in love. Arthur comes to Kilthubber and walks with Mary in the gardens of her home.
Mat announces Christmas morning by beating the famous Knocknagow drum. Among those attending mass at the local church is Henry Lowe, guest of the Kearneys and nephew of their new landlord, Sir Garrett Butler. The villagers wait in a line as the gentry enter first. As the Kearneys sit down to Christmas breakfast, Arthur gives a letter for Mary to Barney, the Kearneys’ hapless servant, in which he explains that he is no longer wishes to become a priest and asks her to come to her window to signal her intentions before he leaves Knocknagow. Diverted by his friends in the kitchen, Barney forgets the letter. As Arthur waits in vain below, Mary chats to Henry. Her father reads a letter warning that Sir Garrett has vested control of his affairs in a ruthless land agent named Pender. Barney remembers the letter from Arthur, who has now departed in despair. Reading it, Mary is overcome.
Pender is introduced explaining to Henry Lowe, whose presence he resents, that those living on the land must be cleared to make room for cattle. At the house of Phil Lahy, a tailor, his wife, Honor, tries to persuade him to finish a new coat which Mat has ordered for the wedding of Ned Brophy. When Mary Kearney pays a visit, Honor appeals to her to distract Phil from drinking; her husband drinks while finishing the coat. While Mat Donovan is collecting the coat, Pender bursts in and abusively demands a light for his lantern. He is physically restrained by Mat, whom he threatens to destroy. Mat pays for his coat and Phil leaves to buy alcohol.
The aristocratic Henry Lowe proposes to Mary, who, still thinking of Arthur, refuses him. Meanwhile, Arthur tells Father Carroll that he has lost his vocation. Carroll recommends that he study medicine and gives the young man his life savings.
Mat leads the Knocknagow team to victory in a hurling match. In a hammer-throwing contest with Captain French, Mat urges himself to best his neighbour’s throw with the words, “For the honour of old Knock-na-gow, I must win!”
Billy Heffernan, a turfman and musician, is welcomed by the Lahys, their son Tommy, and invalid daughter Nora, with whom he is in love.
Maurice Kearney gives Barney a gun to take to Mat Donovan for repair. Pender, eavesdropping, wonders how to exploit the situation. Meeting Peg Brady, a village girl, Barney is distracted from his task and hides the gun behind a wall so as to be able to join Peg in chasing after the local hunt.
Pender instructs his assistant, Darby Ruadh, to begin the evictions in Knocknagow. Mat arrives to remind Pender that he is a freeholder and therefore cannot be evicted: he angrily warns Pender that there will be a day of reckoning. Ruadh and the bailiffs violently evict Mick Brian, a peasant, and his family, and burn their cottage.
Meanwhile, Mat serves as best man at Ned Brophy’s wedding, where Maurice Kearney gives a toast to the newly-weds. Mick Brian, now destitute, discovers the gun and desperately resolves to kill Pender. Instead, Mick is followed by Pender to the Lahy home, where the sight of Nora Lahy saying the rosary persuades him to abandon his plan. Pender observes Mick throwing the gun into a pond.
While out walking, Maurice and Mary Kearney happen across Mat’s sister Nellie as she tends to the Brians. Mick arrives in haste to announce that Pender is now evicting a peasant named Tom Hogan and his son Jimmy, a decorated army veteran. Hogan protests that he has never fired a gun, prompting Pender’s reflection that he will be an easy man to evict. Maurice Kearney offers the Brians shelter in his house.
Father Carroll visits Nora Lahy. Billy, who has been visiting Nora often, recalls a happy occasion when he carried her across the river Anner. He realizes that she is now dying, and breaks down. Later, while delivering turf in the nearby town of Clonmel, Billy meets an English soldier who had been courting Bessie Morris, Mat’s sweetheart, in Dublin the previous year. He reluctantly agrees to take Bessie a pair of earrings from the soldier. Bessie is delighted by the gift but is reproved by Mary Kearney. The soldier comes to Bessie’s house but she does not admit him. Peg Brady, who is also interested in Mat, uses an old letter from the soldier in order to drive a wedge between him and Bessie. Mat confronts Bessie, who petulantly refuses not to see the soldier any more, prompting Mat to declare his intention of going to America.
Mat finds the soldier, no longer in uniform, peering over the wall of Bessie’s garden, and gives him a sound beating. The fight is clandestinely observed by Pender, who devises a scheme to frame Mat for robbery of Sir Garrett’s rents. While Mat, accompanied by Barney, leaves for the emigrant ship, Pender disposes of his now-empty strong box in the same place as the gun.
As he leaves, Mat meets Mick Brian and gives him some money. Pender, who has promised the soldier £200 to help him in the conspiracy, tells the magistrate that he has been robbed by Mat and two masked men. Meanwhile, Mat embarks for America and Barney awakes with a hangover to find himself mid-Atlantic aboard another ship. Back in Kilthubber, Pender tells the magistrate and Maurice Kearney that his assailant was carrying Kearney’s gun.
Henry Lowe arrives at the Butlers’ home in Italy, where Sir Garrett has been describing Knocknagow as an idyll to his daughter, and explains that his authority is being abused by Pender to oppress the people. Mat is arrested in Liverpool and brought back. Billy learns that Barney’s testimony is crucial to proving Mat’s innocence.
Billy joins the Lahys at the bedside of their dying daughter. Phil resolves never to drink again. At the moment of Nora’s death, a linnet which has never before sung calls forth.
Christmas Day finds Mat in Clonmel jail where Billy scales the wall to visit him. Bessie leaves for America to find her father, telling Mary to assure Mat of her faith in his innocence. Billy finds Barney and brings him home. Mat is given a rousing welcome at the Kearneys’, and Mary passes along Bessie’s message. Peg confesses to Mat about the deception of the soldier’s letter to Bessie. Barney consoles Peg by making her laugh and then kisses her.
Sir Garrett arrives to find Pender about to evict the Kearneys for late payment of rent. Arthur proposes to Mary and is accepted. Pender is arrested by the police, to the delight of the Brians. Mat journeys to America, where he meets the Lahys, who tell him that Bessie is living with her father in the “far West”. With some help from Bessie, he proposes and they marry before returning to his cottage. In a final tableau, Mat and Bessie are visited in their home by Arthur and Mary, now married, and Billy.