On a hidden atoll, Princess Lais finds one baby of twin boys born on Bikini island when the atom bomb exploded. The boy, now named Bikini, grows to adulthood in a few months. When a gang raids the atoll, he transforms into his twin brother, the superpowered Atom-Man, by speaking the word 'exenor'. The twins accept their mission to 'battle with the forces of evil to make the atomic era the glory of mankind'!
When the gang returns, Lais' father is fatally wounded and he entrusts Atom-Man with the secret of the atoll. Down a secret path in a hidden cave, Atom-Man meets the Prophet of Exenor, custodian of the world's most terrible secret. In the distant past, a power greater than the atom destroys an entire civilisation. Atom-Man is offered the power's secret formula when need for the fight against evil.
Atom-Man hijacks a plane to take Lais with him from the atoll and then diverts a battleship to destroy the gang who killed Lais' father. Unknown to Atom-Man, the gang leader escapes in a one man submarine.