When world peace is threatened by the emergence of a terrorist group called the Black Cross Army, EAGLE (The Earth Guard League[3]) is formed to combat the threat.

These surviving members are summoned to a secret base located underneath the snack shop "Gon", where they are recruited by EAGLE Japan's commander, Gonpachi Edogawa.

The main headquarters was the flying Black Cross Castle (黒十字城, Kuro Jūjijō), which orbited high above the ground.

The Masked Monsters (仮面怪人, Kamen Kaijin) are the Black Cross Army's field agents, who cause chaos and disorder wherever they go.

The series was adapted into a manga written and drawn by Ishinomori and published in Weekly Shōnen Sunday magazine from May 4, 1975, to August 17, 1975.