Rob Roy, who is one of the farmers on the estate of the Duke of Montrose, is called in by the duke to make an accounting. When the duke questions Rob's figures, that worthy resents it and takes one of the duke's flunkies, who tries to get him out of the room, and throws him out of the window. Rob then returns to the duke, but the duke has called in some soldiers and they overpower the Scot giant. While Rob lies in prison, the duke bums his home and then releases him so that he may see only the ashes. Bent on revenge, Rob Roy goes to Sir Frederick Vernon, who is secretly conspiring against the English, and offers his assistance. The plotters are interrupted in one of their meetings by the entrance of Rashleigh Osbaldistone, the nephew of the wealthy London banker (Sir Osbaldistone). Rashleigh offers to give the conspirators a sure means of freeing Scotland, providing Sir Frederick will promise him the hand of his daughter, Diana, who has just demonstrated her dislike for young Osbaldistone. Sir Frederick is so set upon his purpose of bringing freedom to his land that he forces his daughter to take an oath to marry Rashleigh. Rob Roy witnesses the taking of this oath, although he is not in favor of forcing the girl into such a marriage. In London, Francis Osbaldistone, a young man who prefers to write poetry and dream, rather than work in his father's bank, has given up his place in the bank and he leaves to visit at the Vernon Castle. Rashleigh, his cousin, hears of his leaving and takes the place made vacant in the bank. When Francis arrives at the Vernon Castle he is deeply in love with Diana. A few days later the news comes by Jarvie, Sir Osbaldistone's Glasgow representative, that Rashleigh has stolen some very valuable bonds from the bank, and Francis and Jarvie set out to hunt the thief. They meet Rashleigh in the mountains and Francis and his cousin fight a duel. They are interrupted by Rob Roy, who stops the fight and orders Rashleigh away. He thinks the thief is on an important mission to assist the Scots in their fight for freedom. After Rashleigh has departed, Francis explains the theft of the bonds in his father's bank and then Rob agrees to assist in the pursuit of the thief. Rashleigh, to revenge himself on Francis and place Sir Frederick in his power, turns traitor and goes to the English headquarters, where he tells of Sir Frederick's plot. The English start for the Vernon Castle and Sir Frederick and Diana escape through a secret passage. Francis and Jarvie, not knowing of Rashleigh's treachery, apply to the English for assistance in tracing the thief of the bonds, and they are also placed under arrest. A Scot, who attempts to assist them, is arrested and threatened with hanging if he does not disclose the cave where Rob Roy lives. He refuses and is about to be hung when Rob appears in the distance and signals him to tell. The prisoner then agrees to lead the men and they start with a detachment of troops, taking Francis and Jarvie along as prisoners. Rashleigh discovers Rob Roy, and pretending to be friendly with the Scot leader, he succeeds in securing his sword and then places him under arrest. The English place Rob in a boat and start across the river with him. The detachment of troops who had been following their guide found themselves in an ambush, which had been prepared by Rob's wife, and they were most ingloriously defeated in a great battle there in the hills. Rob escaped by jumping into the river from the boat and arrived just as the Scots, headed by his wife, had routed the English. Francis set out again in pursuit of Rashleigh and met Sir Frederick and Diana, who were fleeing from the pursuing English. The three went to Rob's cave to get Jarvie and here they were surprised by the English, headed by Rashleigh and captured. Rashleigh's triumph was short-lived, however, for Rob's men came in just in time to put an end to Rashleigh's insults to Diana. Rob fought a fair duel with Rashleigh after capturing him and killed him in fair fight, thus leaving Diana and Francis free to wed. The stolen bonds were found in Rashleigh's coat.