Underwater!

While scouring the Caribbean sea floor for treasure, Johnny Grant discovers the remains of a small ship and reports his findings to his Cuban business partner, Dominic Casada, who is manning their boat. Dominic joins Johnny underwater, and together they collect several manmade artifacts near the ship. When they surface, they are greeted by shark hunter Rico Arrera, who has maneuvered his boat next to Dominic and Johnny's. Rico feigns a casual curiosity about Johnny's activities, while Johnny claims he is gathering rocks for a scientific study. Later, in Cuba, Johnny and Dominic reunite with Johnny's wife Theresa and show her the artifacts, which date back to the early seventeenth century. Theresa, who has lived through many failed get-rich-quick schemes with Johnny and Dominic, angrily protests their plan to sell their boat, which they use in the tourist trade, in order to raise money for a sunken treasure expedition. Johnny acquiesces to Theresa's demands, and Dominic apparently accepts defeat and leaves. Once they are alone, however, Theresa yells at Johnny for giving in too easily and hiding his true feelings from her. Dominic, meanwhile, drops by the yacht of an American millionaire but finds only Gloria Warner, the millionaire's distraught secretary. After Gloria explains that her debt-ridden boss abandoned the boat, whose title is under her name, and left her stranded, Dominic convinces her to become his partner. Later, at a nightclub, Gloria and Dominic run into Johnny and Theresa, who reveal that they sold their boat to finance the expedition, and a four-way partnership is formed. Now flush with equipment and supplies, the four are joined on the yacht by Father Cannon, a priest and historian. Once at sea, Father Cannon questions Dominic about the relics, noting that one of them could only have come from a big ship. Dominic admits that he bought the artifacts from a fisherman, who had found them in the vicinity of the sunken ship, and scattered them around to entice Johnny. Father Cannon then states that the ship was probably the pilot vessel of a convoy that fled Panama with a gold statue of the Madonna, which sank during a hurricane. Thrilled at their prospects, Johnny and Theresa dive the next day and find a second ship, a man o' war. Later, the group discusses the probable location of the treasure ship and are disturbed when Rico and his crew, Miguel and Jesus, reappear. Rico obviously does not believe Johnny's rock hunting story, but leaves without incident. Dominic and Johnny then dive and spot the treasure ship lodged on a coral cliff. That evening, Theresa, who has already sensed a growing obsession in her husband, suggests that they picnic on a nearby island. Their romantic plan is spoiled, however, when Dominic and Gloria insist on joining them. On the beach, Johnny tells Theresa about his dreams to travel the world with her, and the two happily contemplate a new life. The next day, Dominic and Johnny, a former Navy explosives expert, return to the treasure ship and set dynamite to blast open a sealed door. Although the explosion rocks the ship, the door falls off and stacks of gold bullion are discovered. While Johnny is carrying some of the gold up to the yacht, Dominic suddenly becomes ill and loses consciousness. Dominic revives before any harm is done, but Johnny realizes that the middle-aged Dominic is no longer strong enough to dive. Johnny then devises a plan to pull a second door open by means of a hook and rope and, despite Dominic's near miss, both men go under to implement it. While they work on the door, the fragile ship starts to break apart and Dominic is buried in sand. Johnny rescues him, and once back on the surface, Dominic tells Father Cannon that, before being buried, he felt the Madonna statue and shows him a gold sphere the broke off from its hand. Soon after, Rico and his men return, and when Rico asks to confess to Father Cannon, the group allows him on board, then extends a dinner invitation. The dinner is tense but cordial until Rico finally confronts the group about the treasure. A fight breaks out, but Rico and his men are subdued and dumped on the island. Disturbed by the confrontation, Theresa begs Johnny to quit, but he refuses to give up his dream. The next day, Theresa insists on diving with Johnny, and during the pulling operation, the ship timbers crack and fall, pinning Theresa. When the engine pulling the rope stalls, Johnny surfaces to fix the problem, and Dominic dives in to help. Although Johnny and Dominic free Theresa, the ship breaks apart, and Dominic narrowly escapes with his life. As soon as they return to the ship, they are greeted by a gun-toting Rico, Jesus and Miguel, who were brought back from the island by Gloria. Rico demands the gold, but Johnny wrests a rifle away from Jesus and trains it on Rico. To end the impasse, Johnny offers Rico some of the gold. After Rico accepts his share and departs peacefully, Dominic tells Father Cannon that the statue is lost forever. Johnny then embraces a relieved Theresa, and they all head back to Cuba with the remaining gold.