About the book (from Wikipedia):
Frank Osbaldistone narrates the story. He is the son of an English merchant who parted from his family home in the north of England near the border with Scotland when he was a young man, being of different religion and temperament than his own father or his younger brother. Frank is sent by his father to live at the long unseen family home with his uncle and his male cousins, when he refuses to join his father’s successful business. In exchange, his father accepts Frank’s cousin Rashleigh to work in his business. Rashleigh is an intelligent young man, but he is unscrupulous, and he causes problems for the business of Osbaldistone and Tresham. To resolve the problems, Frank travels into Scotland and meets the larger-than-life title character, Rob Roy MacGregor.