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 fabuous value that has been the dream and hope of roving adventurers along the Spanish Main for many years.
