“TAKEOVER OF THE EARTH-MASTERS.” Misinterpreting a radio telescope message from Earth, alien beings known as the Adaptoids believe the members of the Justice League to be super-powered tyrants, and decide that they are a threat that needs to be exterminated!
The Flash responds to a crisis, on the outskirts of Central City. With no place to go, the Hawkman lingers, for hours, on board the Justice League of America's satellite headquarters. Aquaman attempts to convince the Hawkman that he should leave. Spying the Flash's situation, the Hawkman, prematurely, summons the Justice League of America. Tied up with personal matters, Bruce Wayne, and Ray Palmer, are unable to respond. Aquaman, the Black Canary, the Red Tornado, and Superman join the Flash in Central City. While Aquaman explains why the Hawkman sent the signal, the Flash is ambushed by the strange, protoplasmic creatures he was investigating.
The Black Canary teleports back up to the satellite, with the Flash, to get the Scarlet Speedster medical aid. The Justice League of America battle the protoplasmic creatures. The bizarre aliens undergo a molecular change, and begin broadcasting kryptonite radiation at Superman. The creatures also override Aquaman's telepathic commands, taking control of the marsh life fighting on his behalf. The creatures undergo an evolutionary metamorphosis. Having adapted to the Justice League of America's powers, the creatures render the team unconscious. Upon recovery, the Justice League of America reassemble, on board their satellite headquarters.
The Flash reveals that a radio-astronomer, Doctor Hubbard, received a strange message, in English, from deep space. The message stated that help, in the form of the Adaptoids, was on it's way. A day later, the alien creatures descended on the outskirts of Central City. In his frustration to contact alien life, Hubbard accidentally sent a garbled message out. Said message led the receiver to believe that the Earth was menaced by super-beings. This alien receiver then dispatched the Adaptoids to deal with the situation. Before departing terrestrial space, the alien master of the Adaptiods issues an ultimatum to the Justice League of America... depart the Earth or be destroyed.
With the Adaptoids concentrated in three different locales, the Justice League of America splits into teams to deal with the threat. Clearly distracted by his current situation, the Hawkman is left behind, to coordinate the team's efforts from the satellite. The Black Canary, and the Flash, confront the Adaptoids in Hong Kong. The Flash slams headlong into an invisible barrier, at top speed, suffering a concussion. The impact also causes the Black Canary to break her leg. The Black Canary uses her sonic scream to keep the Adaptiods at bay, long enough for her to reach the Flash. The Black Canary, with the Flash, teleports back to the satellite.
Superman confronts the Adaptiods in San Francisco. Overwhelmed by the Adaptoids, Superman, too, teleports back to the satellite. Aquaman, and the Red Tornado confront the Adaptoids in Venice. Both heroes meet with defeat. Aquaman suffers the worst of it, as he is transformed into a merman. The Red Tornado teleports, with Aquaman, back to the satellite. Upon their arrival, the Justice League of America find their satellite headquarters empty. The Hawkman has failed to summon the rest of the team. Worse, the Hawkman has, seemingly, abandoned his comrades, returning to Thanagar, to be reunited with his wife.