Rob Roy

In Scotland, 1713, Robert Roy MacGregor (Liam Neeson) is the Chief of Clan MacGregor. Providing the Lowland gentry with protection against cattle rustling, he barely manages to feed his people. Hoping to alleviate their poverty, MacGregor borrows Â£1,000 from James Graham, Marquess of Montrose (John Hurt) in order to trade cattle.
Impoverished London aristocrat Archibald Cunningham (Tim Roth) has been sent to stay with Montrose, who it is implied is related to him, as his debaucheries have become a problem back in England. Cunningham learns about MacGregor's loan from Montrose's factor, Killearn (Brian Cox) and murders MacGregor's retainer Alan MacDonald (Eric Stoltz) to steal the money. MacGregor requests time from Montrose to find MacDonald and the money. Montrose offers to waive the debt if MacGregor will testify falsely that Montrose's rival John Campbell, 2nd Duke of Argyll (Andrew Keir) is a Jacobite. MacGregor refuses and Montrose vows to imprison him in the tolbooth until the debt is repaid, but MacGregor flees, briefly taking Cunningham hostage. Montrose decides to seize MacGregor's land to cover the debt, declaring him an outlaw and orders Cunningham to bring him in "broken, but not dead". With MacGregor in hiding, redcoats slaughter MacGregor's cattle, burn his croft, and Cunningham brutally rapes his wife Mary (Jessica Lange). Mary understands that Cunningham's intent is to flush her husband out of hiding and makes his brother Alasdair, who arrives too late to save her, swear to conceal knowledge of the incident from him. Unaware of the assault on his wife, but the damage to his property being all too evident, MacGregor refuses to permit his outraged clan to wage war on Montrose. Instead, he decrees, "The tenderest part of the Marquess is his purse. We'll hurt him there. Thieve his cattle, steal his rents."
It transpires that Betty (Vicki Masson), a maidservant at Montrose's estate, has become pregnant with Cunningham's child. When Killearn tells Montrose, Betty is dismissed from service and contemptuously rejected by Cunningham. A heartbroken Betty seeks refuge with the MacGregors, and reveals that she had overheard Killearn and Cunningham plot to steal the money. To build a case against Cunningham, MacGregor abducts Killearn and imprisons him on Factor's Island. Mary promises Killearn that he will be spared if he testifies against Cunningham, but Killearn taunts her with her rape as it becomes clear to him that MacGregor knows nothing about it. Realising that Mary is pregnant, he threatens to tell MacGregor that Cunningham may be the father if she does not drop her case against him. Enraged, Mary draws a sgian dubh and stabs Killearn in the neck. Alasdair thus pursues him and drowns him in the loch.
Montrose makes clear to Cunningham that he suspects who really stole the money but that he doesn't care. Complaining that the ongoing thefts of his cattle and rents will impoverish him and mystified by the disappearance of Killearn, he orders Cunningham to again pursue MacGregor so as to prevent further humiliation. Cunningham and the redcoats systematically burn the Clan's crofts. MacGregor refuses to take the bait, but Alasdair attempts to snipe Cunningham and hits a redcoat, revealing their hiding place. The redcoats attack and they shoot both Alasdair and another Clan member, Coll. With his dying breath, Alasdair finally tells MacGregor about Mary's violation by Cunningham. Taken prisoner, MacGregor accuses Cunningham of murder, robbery and rape. Cunningham confirms the charges, taunting him that he enjoyed Mary far more than the women who slept with him willingly. The following morning, Montrose, despite hearing MacGregor confirm his suspicions as to where his money really went, orders MacGregor to be summarily executed by hanging from a nearby bridge. MacGregor manages to loop the rope binding his hands around Cunningham's throat and then jumps off the bridge. To save Cunningham, Montrose orders the rope to be cut, freeing MacGregor. MacGregor is chased downstream by the redcoats, but he evades them by hiding inside the rotting corpse of a Highland cow. Cunningham, meanwhile, survives his strangulation, but his vocal chords are severely damaged.
Mary, during this time, gains an audience with the Duke of Argyll and exposes Montrose's plan to frame him. Moved by MacGregor's integrity, he grants the whole family asylum at Glen Shira, on his estates. MacGregor arrives at Glen Shira, at first upset by Mary's unwillingness to inform him of her assault or her pregnancy. However, even in light of the unborn baby's possible paternity, he comments, "It's not the child who needs killing." The Duke, though sceptical of MacGregor's likelihood of survival, subsequently arranges a duel between MacGregor and Cunningham, wagering Montrose that if MacGregor lives, his debt will be forgiven and that if he dies, the Duke will pay his debt. Montrose agrees to these terms and Cunningham and MacGregor vow that no quarter will be asked or given. Armed with a smallsword, Cunningham skillfully attacks and repeatedly wounds MacGregor, who, already labouring from the injury of his previous capture, appears to swiftly exhaust himself swinging a heavy broadsword. A gloating Montrose signals Cunningham to finish him, but MacGregor grabs his enemy's sword-point with his left hand. As Cunningham struggles to free his blade, MacGregor's seizes his dropped weapon and delivers a fatal strike. His honour restored, MacGregor vows that he will never leave his family again.

Question: Who exposes Montrose's plan to frame the Duke of Argyll?
Answer: Mary