In the world of the 31st Century and the city of New Modernia, a shape-shifting race called the Chameleons have appeared, and they are so great a peril to society that Professor Ellery approaches the Mayor and City Council. He proposes that he take a Time-Bus back to the 20th Century to get the Justice Society involved in the matter and bring them back to the 31st Century. The JSA, after having encountered a Chameleon, agree.; The JSA arrive in the 31st Century and are led into a chamber housing giant homicidal robots by a person they believe to be Professor Ellery, but who is actually a Chameleon. When the "Professor" leaves the room, Knelo pushes a button activating the robots. The JSA finally defeats them, then seeks the Chameleon Chief, who has fled. Learn the Chameleons plan to impersonate three officials, so they divide up into teams to find and protect the three men. Flash and Wonder Woman head to City Hall, but they face a Chameleon disguised as Mayor Hoving, who escapes with the Great Seal.; Two scientists have constructed the Triple-Z Bomb, so powerful that it can blow up the Earth. General Cadwell, actually a Chameleon, tells them to take the bomb to a deserted area and bury it. G.L. and the Atom grab the "General", but must fight the guards, which allows the "General" to escape. Meanwhile, Hawkman, Dr. Mid-Nite and Black Canary arrive at Spaceships, Inc. looking for C. F. Tanner, and discover him in a forbidden area of the facility. The team finds "Tanner" about to board a Skyblaster and are ready to apprehend him when plant guards fight the JSA, allowing "Tanner" to escape.; Knelo issues a proclamation, officially sealed, warning all Earthlings to surrender or be blown to pieces by the Triple-Z Bomb. As three real officials contemplate surrender, Black Canary tells them not to as the other JSA members are preparing to attack the Chameleons in disguise as them. Unknowing, Knelno sees them approach, and who suddenly doff their disguises as G.L. renders the Triple-Z Bomb harmless. Knelno's attempt to use the robots fail and the Chameleons are placed in the Skyblaster and shot into space, unable to return for 100 years. The JSA then returns to 1950 via a time tunnel.