Martin Conisby, embittered by his five years of slavery on the Spanish galleon Esmeralda, escapes during a sea fight and makes his way back to England, determined to avenge himself on Richard Brandon, who was the cause of his father's death and his own ill-treatment. Broken in body and spirit, he arrives home just in time to save from the hands of robbers a beautiful girl, Lady Joan Brandon, the daughter of the man whom he has sworn to punish. In a tavern he meets a pal, Adam Penfeather, who unfolds to him the story of Black Bartlemy, an infamous pirate, and his treasure buried on an island—treasure of fabulous value that has been the dream and hope of roving adventurers along the Spanish Main for many years.