The first part of the book recounts the attempts of the hero - David Balfour - to gain justice for James Stewart - James of the Glens - who has been arrested and charged with complicity in the Appin Murder. David makes a statement to a lawyer, and goes on to meet Lord Prestongrange - the Lord Advocate - to press the case for James' innocence. However his attempts fail as he is once again kidnapped and confined on the Bass Rock - an island in the Firth of Forth - until the trial is over, and James condemned to death. David also meets and falls in love with Catriona MacGregor Drummond, the daughter of James MacGregor Drummond, known as James More, also held in prison, whose escape she engineers. He also receives some education in the manners and morals of polite society from Barbara Grant, the daughter of Prestongrange.
In the second part David and Catriona travel to Holland, where David studies law at the University of Leyden. David takes Catriona under his protection (she having no money) until her father finds them. James More eventually arrives and proves something of a disappointment, drinking a great deal and showing no compunction against living off of David's largesse. At this time, David learns of the death of his uncle Ebenezer, and thus gains knowledge that he has come into his full, substantial inheritance. David and Catriona, fast friends at this point, begin a series of misunderstandings that eventually drive her and James More away, though with David sending payment to James in return for news of Catriona's welfare. James and Catriona find their way to Dunkirk in northern France. Meanwhile, Alan Breck joins David in Leyden, and he berates David for not understanding women.
It’s this way about a man and a woman, ye see, Davie: The weemenfolk have got no kind of reason to them. Either they like the man, and then a’ goes fine; or else they just detest him, and ye may spare your breath - ye can do naething. There’s just the two sets of them - them that would sell their coats for ye, and them that never look the road ye’re on. That’s a’ that there is to women; and you seem to be such a gomeral that ye cannae tell the tane frae the tither.
Prodded thus, and at an invitation from James More, David and Alan journey to Dunkirk to visit with James and Catriona. They all meet one evening at a remote inn, and discover the following day that James has betrayed Alan (falsely convicted of the Appin murder) into the hands of a British warship anchored near the shore. The British attempt to capture Alan, who flees with David and Catriona, now reconciled and shamed by James More's ignominy. The three flee to Paris where David and Catriona are married before eventually returning to Scotland to raise a family.
Although 'Catriona' may not have gained the popularity that was achieved by 'Kidnapped' it is, in some ways, a more intriguing work than it's predecessor. While the story is a straightforward continuation of David Balfour's adventures, there is also a wealth of incidental detail included in the tale - some of which is quite enigmatic. In part one of the book, the author identifies several days of the week, along with their corresponding dates. It's evident that he took some care to detail the correct sequence of days as the story progresses. Given that Stevenson made the effort to ensure continuity, it's a minor mystery that those particular days and dates are not correct for the year in which he has set the novel. Whether by chance, or by design, Stevenson selected days of the week and dates that would be appropriate for the year 1752 - provided the Gregorian calendar is used as a reference. However, the riddle doesn't end there because the Gregorian calendar was not officially established in Britain until September of 1752. Stevenson's precision in describing some of the locations in the story, is another intriguing aspect of the novel. Much of it may be attributed to nostalgia for the old haunts of his youth. However, there are other details which are not so readily explained because he also describes minor local features that were long gone by his time. Their inclusion suggests that he must have undertaken a fair amount of research to ensure that settings were authentic. Similar treatment is applied to some of the minor characters in the novel. There's nothing very unusual in an author threading real places, or real people, into the fictional weave of a tale. What is more unusual, in the case of Stevenson, is that he also did that with locations and characters that are really quite incidental to the story. As one example, in chapter XIV of 'Catriona' he briefly introduces Captain Palliser and the ship - HMS Seahorse. For the few sentences involved, any fictional captain or ship might have served as well - and yet Stevenson selected a genuine historical figure for that brief appearance. (Though, in fact, the real Hugh Palliser didn't sail in that region until the year 1754).
The reasons behind it all seem to be something other than an obsession with verisimilitude. Stevenson himself wrote, in his introduction to 'Kidnapped'… "..it is more honest to confess at once how little I am touched by the desire of accuracy. This is no furniture for the scholar's library, but a book for the winter evening..."
Perhaps the only clue lies in the opinion of friends who knew him, for it was said of Stevenson that he had a mischievous sense of humour…