Fanny Campbell is a fiery 18-year-old farm girl in pre-Revolutionary War Rhode Island. Her parents taught her to sail, hunt, fish, ride, fight with broadswords, and be an independent thinker. Those qualities make everyone in her small village sure she will be an old maid until a wild storm blows Will, a young naval officer, into her life. He is immediately attracted by her fierce independence and strength. After a spirited courtship involving footraces, sword fights, and pranks, they marry, and too soon, Will's ship puts back out to sea.

When she learns that Will's ship has been captured by the Spanish and he and his crew have been imprisoned in Cuba, Fanny disguises herself as a man, signs on to a broken-down merchant ship, and goes to sea to rescue him. Along the way, she signs on to the pirate crew of the Bloody Rose and thus begins Fanny's epic adventure as an accidental pirate.