During a motocross race, Takeshi Hongo, the cyborg hero Kamen Rider 1, and his ally, FBI agent Kazuya Taki, are caught in a sudden ambush by the terrorist organization Shocker. Explosions from a Shocker helicopter appear to consume them, and they are presumed dead. In truth, they survive and eliminate their attackers, disguising themselves in Shocker uniforms to infiltrate the enemy's main headquarters. Their deception is short-lived; the Shocker executive known as Jigoku Taishi, or Ambassador Hell, quickly detects the intruders and seals them inside a chamber filling with deadly gas. Before triggering the base's self-destruct sequence, Jigoku Taishi taunts them by revealing Shocker's ultimate plan: the completion of a Super Destruction Light Beam, a giant laser weapon powerful enough to annihilate entire cities. Kamen Rider 1 and Taki narrowly escape the explosion and learn that their mentor, Tobei Tachibana, along with members of the racing club, have been kidnapped by Shocker's minions. The heroes now race against time, facing a gauntlet of revived monsters including the praying mantis-like Kamikirikid, as they must rescue their friends and prevent the laser from destroying Tokyo Tower from the organization's secret base on Mount Fuji. Jigoku Taishi, a sadistic and high-ranking commander who can transform into the rattlesnake monster Garagaranda, orchestrates this operation as part of Shocker's ongoing campaign for world domination. The film concludes with Kamen Rider 1 confronting the monstrous army, destroying the weapon, and defeating Kamikirikid, while Jigoku Taishi narrowly escapes to continue his vendetta against the Riders.