The evil organization Shocker alters history by sending their newest creation, Kamen Rider 3, to defeat Kamen Riders 1 and 2 back in 1973. In the alternate present, Shocker is more powerful than ever, and most of the Kamen Riders are now either imprisoned or brainwashed to work for them. One such brainwashed Rider is Shinnosuke Tomari, who, thanks to his partner Kiriko Shijima, remembers the truth and joins forces with the remaining Kamen Riders who are still at large to make a stand against Shocker and put history back on its proper course.