Following another disappointing fishing expedition off the Florida coast, Greek-American sponge fisherman Mike Petrakis, his son Tony and the rest of the crew on board the Aegli return home to Tarpon Springs, where they are greeted by Mama Petrakis and Tony's sister Penny. Also waiting for them at the dock is money-lender Demetrios Sofotes, who is eager to get a payment toward the money that he invested in the Aegli . Mike and his crew are further disappointed when they learn that another boat, the Helios , is bringing in a profitable catch after sponge-fishing the dangerous Twelve Mile Reef. At a Greek Orthodox Church Epiphany festival held on boats anchored at Tarpon Springs, Tony receives a special blessing for himself and his family after winning an underwater diving contest. Tony uses the victory to extract a promise from his father to let him dive on the next expedition. Believing that the waters around Tarpon Springs are no longer good for sponge fishing, Mike decides to break with tradition and take his boat out to Key West, a region unofficially designated off-limits to Greeks. In the Keys, as the Aegli crew brings in a great catch of sponges, two American sponge fishermen, Arnold Dix and Griff Rhys, approach in their small boat, grab Mike's air line and threaten to cut off his air unless the Greeks give them their sponge catch. Tony and the others comply with the demand, but later seek out the thieves at Key West. There, Mike and the rest of the Aegli crew go to a café and make believe that they are joining in the celebration of the day's great catch. Meanwhile, Tony falls in love with Gwyneth Rhys, Arnold's sweetheart, and shares a dance with her. Arnold becomes jealous, and during an ensuing brawl, Tony and Gwyneth sneak off to a nearby park, where they kiss. The Aegli crew eventually gets its revenge when Mike subdues Arnold and forces him to eat a cigar. For the next expedition, Mike takes the Aegli to the Twelve Mile Reef, but tragedy strikes during a dive when Mike slips on the reef, loses compression and is propelled to the water's surface too fast. Mike gets the bends from coming up too fast, and later dies. While Tony wanders off to mourn, Arnold and Griff loot the Aegli , and another group of American fishermen scuffles with Tony's uncle Socrates "Soak" Houlis, and set the boat ablaze, nearly destroying it. Gwyneth then takes Tony to see her father, Thomas, a fair man who orders Arnold and his gang to pay Tony for the stolen sponges. Furious at Thomas' order, Arnold goes after Tony and gives him a beating. The injured Tony makes his way back to the dock, where he and Gwyneth steal a boat, the Conch , and head out to sea. Gwyneth, more in love with Tony than ever, gets an idea to turn the Conch into a deep sea diving boat, and they begin sponge fishing at the Twelve Mile Reef. Arnold and his compatriots eventually find Tony and Gwyneth and engage them in a bruising fistfight. The struggle forces Tony and Arnold into the water, and when Arnold becomes entangled in kelp, Tony rescues him. Arnold is grateful to Tony for saving his life and the two adversaries make amends. Gwyneth decides to marry Tony, and her family and Tony's join together to arrange a festive wedding.