The trio of brave friends who make up Shark, Inc.—Luke, Maribel, and Sabina—dive back into adventure in this follow-up to bestselling author Randy Wayne White’s Fins. Marine biologist Doc Ford invites Maribel, Luke, and Sabina to a remote island in the Bahamas where lionfish, a beautiful and venomous inhabitant of the South Pacific that has invaded Florida and the Caribbean, are not just upsetting the balance of nature by damaging the coral reefs—their sting has put several people in the hospital. What Doc and Captain Hannah Smith don’t mention is that the island is riddled with limestone caves, once home to a band of pirates, and stories of Spanish gold have lured outlaw treasure hunters to the area. When the trio finds precious artifacts, they agree to guard the secret until they’ve thoroughly explored the spot. Soon, outlaws search for the trio, hoping they will lead them to riches.