Red Marlo, one of the original crew members of The Sage, learns that their sunken shrimp boat, La Saga, has been discovered by French marine archaeologists who are searching for La Gallega, one of Columbus's caravels that sank near the mouth of the Rio Belen. Red convinces the Sage crew to embark on a third and final quest for the Spanish treasure hidden in the hold of the sunken shrimp boat. They purchase a tuna boat, head for Panama, and offer their salvage services to the French scientists. The efforts of the Sage crew to raise La Saga are thwarted by technical problems. Adding to their difficulties are the curiosity of a husband and wife who fly in supplies to the French camp and who alert their old adversary, Guillermo Castillo, now a PDF Lieutenant, to their presence.