Submarine Capt. Casey Abbott (Ronald Reagan) is given the perilous mission of stopping the flow of supplies between China and Japan. He rises to the occasion, but his job is complicated when a diver who's got his eye on Abbott's paramour (played by former first lady Nancy Reagan, then known as Nancy Davis) lands in grave danger. Abbott must find a way to keep his personal feelings in check and save the diver in this World War II drama.