The tale unfolds in early 18th Century Scotland, where a band of Scots highlanders embarks on a mission to track down a rival clan that has absconded with cattle belonging to a local lord. Leading this group is Robert Roy MacGregor, portrayed by Liam Neeson, who is fiercely committed to protecting the lord's property, including valuable livestock.
As they pursue the thieves, one of MacGregor's men, Alan McDonald, notes they are likely a day behind their quarry. Eventually, the search party discovers the thieves camped out in a secluded valley. Given the precariousness of a night attack, MacGregor instructs his men to rest. He plans to approach the thieves at dawn to negotiate their surrender. When Alan expresses skepticism about the effectiveness of words, Rob confidently asserts, “I know one of them.”
The next morning, Rob honors his word and confronts the thieves in their camp. He boldly claims that the cattle belong to his lord and that everyone will live if they surrender peacefully. To emphasize his authority, Rob commands his men to reveal their positions surrounding the camp. The leader of the thieves, Sibbald, laughs off Rob's demands, but when he attempts to kill Rob, he meets his own end instead. The remnants of Sibbald's group are spared, and they hastily vacate the area. Rob returns home to his proud wife, Mary, played by Jessica Lange, and their two young sons. In the bliss of their reunion, Rob and Mary share an intimate moment beneath a tree.
Their village is under the watchful protection of John Campbell, Duke of Argyll. During a sword match featuring Campbell’s finest duelist, Guthrie, the Duke meets with the ambitious Marquis of Montrose, who is accompanied by the flamboyant Archibold Cunningham. After a challenge is laid down, the duel unfolds, with Archie surprising everyone by easily overpowering Guthrie, leading to significant wagers won for Montrose.
In the meantime, Rob devises a plan to increase his fortunes through cattle droving. He seeks a loan of 1000 guineas from Campbell to purchase cattle at a port. Rob believes that if successful, he can later sell the cattle back at a profit to Campbell. Campbell advises Rob to formalize the loan through Montrose.
However, events take a darker turn when Killearn, Montrose’s banker, conspires against Rob. He informs Archie about Rob's loan, setting the stage for a treacherous theft of the money intended for MacDonald. On the fateful day, Killearn intentionally delays MacDonald’s access to the loan and ultimately forces him to accept coins instead of the agreed-upon credit slip.
As MacDonald attempts to deliver the money to Rob, he falls into a trap set by Archie, who murders him and absconds with the funds. When MacDonald fails to return, Rob confronts Killearn, who deceitfully suggests his companion has betrayed him. After failing to convince Montrose of his innocence in a desperate plea for more funds, Rob is branded a fugitive.
With mounting tensions, Rob confides in Mary about the situation, leaving her behind with loyal protection. Yet, this doesn’t shield Mary from the approaching threat when Archie and his henchmen arrive. In a violent outburst, Archie drags Mary into their dwelling and commits a horrific act against her. After the assailants depart, Mary grieves but fiercely instructs her brother Alasdair to remain silent about the violation, not wishing for Rob to avenge her honor.
Determined to restore Rob’s name, Mary concocts a plan. Discovering Archie's lover, Betty, who is pregnant with his child, Mary persuades her to testify against Archie. Tragically, however, Betty takes her own life before the truth can be revealed.
Filled with a rage that fuels her quest for justice, Mary confronts Killearn. In a chaotic struggle, she fatally wounds him, seeking to clear Rob’s name while deepening their bond in the face of evil. Meanwhile, Rob is captured by Archie, enduring humiliation and hardship, even as he plots his revenge.
At the climactic moment by the Bridge at Glen Orchy, Rob seizes a harrowing opportunity to turn the tables on Archie during their trial. Wrapping the ropes that bind him around Archie’s neck, Rob plunges into the river below, narrowly escaping with his life.
In a daring display of resilience, Rob later reunites with Mary, seeking her forgiveness and support. He prepares for a much-anticipated duel against Archie, where their fates will be irrevocably intertwined. As he faces the formidable adversary, Rob recalls the stakes of love and honor, and in an unexpected surge of power, he claims victory in the fight for justice.
With the debts cleared and a promise fulfilled, Rob returns to an ecstatic Mary, ready to embrace their future.
