Through a series of mishaps, caused by his desire to do the right and honorable thing, Peter Blood, Irishman, soldier, graduate of Trinity College in Dublin, and doctor, goes to the aid of a well-born client who was wounded in an act of rebellion for which the doctor has no sympathy. While the aristocratic leaders of the rebellion buy their freedom, Blood is condemned for aiding the rebels and, with the others from the lower classes, is transported to Barbados as a slave. After escaping, he comandeers a Castilian warship and becomes a pirate.
Through his pirate days, he retains those qualities of all Sabatini heroes: honor, dignity, intelligence, a quick wit, and a hidden love for an impossible woman.
While the Errol Flynn movie is mostly true to the plot and the spirit of the novel, it leaves out a great deal and, of necessity, simplifies Blood's character. If you've seen the movie, read the book anyway. You won't regret it.