David arrives at the House of Shaws and is greeted by Ebenezer pointing a blunderbuss out the window at him, demanding to know what he wants. David convinces him to let him in, and it turns out that he's David's uncle- brother to his late father. Ebenezer is a penny-pinching, paranoid old coot, and David instinctively distrusts him, with good reason as it turns out.
While perusing his uncle's books, he finds one given to Ebenezer by David's father on uncle's fifth birthday. David his father's writing on the inscription, which confuses him, because it's the writing of an older child. Since Ebenezer inherited, however, he must have been- at the age of five- the elder brother. Curious, he questions his uncle, who stalls for time, then makes a rather passive attempt to orchestrate David's "accidental" death. Infuriated by the attempt on his life and suspecting it was to keep him from inheriting, David confronts his uncle who has- or feigns having- some sort of attack. He begs David to let him rest until the morning, when he promises he'll explain everything.
Soon, David is pressed into service as cabin boy when Ransome is killed by the monstrous first officer Mr. Shaun in a drunken rage. Things are looking very bleak for David until he meets Alan Breck Stewart. Stewart ends up on the ship when it runs over the boat he is travelling in, killing everyone on board except Alan, who manages to jump into their rigging.
This is where it gets a bit more complicated if you aren't familiar with Scottish political history. Stewart is a Jacobite, a Scotsman rebelling against the British crown. Following the disastrous Rising of 1745, the Stewarts were punished by having their clan's rent money given over to the Campbells, who had sided with the Crown. When the boat accident occurred, Alan was, in defiance of this edict, taking rents from his clansmen to their Chief who is living in exile in France.
This marks the beginning of David's Highland adventure, as he must travel through this unfamiliar environment, find Alan Breck Stewart, and make his way back to the Lowlands to confront his uncle. To complicate matters, David-caught in the wrong place at the wrong time- ends up accused of murder, with a price on his head, fleeing from the soldiers of the Crown with Stewart.