A strange alien crash results in the emergence of numerous starfish parasites that attach themselves to and manipulate the populace, all while the enigmatic herald known as Starro the Conqueror schemes to subjugate and enslave every form of life throughout the cosmos, which leads to the unification of Superman, Batman, Wonder Woman, the Atlantic king of the underwaters Aquaman, and the Flash, who are summoned by the telepathic extra-terrestrial Martian Manhunter to establish the Justice League, with the hope of countering this immense cosmic menace.
