Ballinrobe, County Mayo, Ireland, 1880. The impoverished population are suffering onerous rents. A bailiff is murdered as the Killain family (Mark and children Anne and Billy) arrive in a postal carriage. Father McKeogh tells militant teacher Daniel McGinty that the landlord Captain Boycott's bailiff Watty Connell has been serving eviction notices on farmers.
Anne discovers that a sack of grain addressed to Hugh Davin conceals a gun, but ties it shut without saying anything. Davin himself hails the carriage and persuades the postman to hand the sack over. Returning to his farm, he finds Connell asking after the form of his horse Corrib Lad.
McGinty trains a group of villagers in military discipline. Davin arrives with the gun, but McGinty points out that they only six guns for forty men. Davin says that there are more effective ways of dealing with bailiffs.
At the county fair, Davin is quizzed by policemen in seach of Connell, who has gone missing. Anne provides an alibi, and later tells him that her brother was shot dead in similar circumstances. Davin wonders if she thinks he murdered Connell. After they part, Anne finds Connell talking to her father.
A village delegation meets Captain Boycott, who refuses to compromise, saying they should increase their land's value by working it harder. Connell advises Boycott that repossessed farms should be reoccupied.
Boycott's evictions are enforced, and Michael Fagan's farm is sacked. Fagan swears revenge on anyone who moves in.
Davin chairs a meeting during which Charles Stewart Parnell, the politician supported by the Irish Land League, is denounced. News arrives that Killain has moved into Fagan's farm, and Fagan suspects Davin's involvement, given his interest in Anne and the fact that the bailiffs ignored his own property.
Davin expresses his concern to Anne, who tells that her family had been evicted three years earlier and that her brother died defending them. Davin tells her that she's either with the community or against it. He notices a threatening notice pinned to the door.
Father McKeogh preaches a sermon in which he urges non-violence and that the villagers attend a political rally. Parnell gives an inspiring speech, exhorting them to resist unjust treatment and to deal with people who exploit others' misfortunes by shunning rather than shooting them.
Captain Boycott rides home to his house, Lough Mask, to find his servants gone. He catches a maid, Bridget, trying to sneak out, and she admits Davin told them to leave. Boycott goes to the pub and is told that no-one will work for him any more. He writes a letter to The Times, which catches the public imagination. Volunteers offer to help gather his crops. 40,000 troops are sent to protect them, and set up camp in Lough Mask's grounds. McGinty denounces Parnell's peaceful methods.
But after three weeks, Boycott's crops have still not been gathered. He also hears that his horse, Prince, has broken his fetlock: he was counting on his racing prowess to resolve his financial difficulties. Connell says that he knows another fine horse.
Fagan 'borrows' Davin's gun in his absence. Davin runs to warn Anne. After they have made sure her father is safe, Davin confesses his love for her. Boycott's men break into Davin's farm and confiscated his property. Corrib Lad is sold to Boycott at auction for five pounds, since no-one else will participate.
At the race, an angry crowd boos Boycott, who is riding the horse himself. Troops move in front of the stands, but this doesn't prevent the mob invading the track after Boycott gains the lead.
Killain is shot by Fagan, but drowns him in retaliation. McGinty urges the villagers to rise up against the Killains. Davin runs to Lough Mask to steal his horse back to get to the farm ahead of the mob. He is captured, but persuades Boycott to co-operate by telling him that if Killain is killed, he will be personally responsible.
Davin arrives at the farm to find Killain dead from Fagan's bullet. He tells the crowd, and Father McKeogh points out the departing army. Boycott was defeated through peace, not violence - and their methods contributed a new word to the English language: "to boycott".
