Dr. Oki, a brilliant scientist who created a new sort of submarine, has vanished. Susumu, his son, detects an unknown group's sinister plot. He is completely familiar with his father's submarine, the "Super 99," including its equipment, weaponry, operations, and capacity. Susumu believes that the only way to find his father is to expose the hidden group Helmet Party and put an end to their plot. He embarks on an undersea expedition with the support of his pals and the Marine Corps, unaware of the dangers that await him...