Fish--nicknamed for his incredible swimming abilities--is a twelve-year-old boy from a poor farming family. After taking a job as a courier for his uncle, Fish is waylaid by pirates, who steal the package he's carrying. He soon learns that it's the key to locating the Chain of Chuacar, a legendary treasure. As he works to earn the trust of Cobb, the fortune-hunting captain of the Scurvy Mistress, Fish learns of a mutiny headed by a nasty pirate called Scab. With time running out to find the Chain, Fish and some fellow shipmates still loyal to Cobb must thwart Scab's dastardly plan.