Justice League of America [Wonder Woman [Diana Prince]; Aquaman [Arthur Curry]; Superman [Clark Kent] (cameo); Green Lantern [Hal Jordan]; Batman [Bruce Wayne] (cameo); Flash [Barry Allen]; Martian Manhunter [J'onn J'onzz]] (first appearance); Starro; Steve Trevor (cameo); Captain Harding (cameo)
Peter the Puffer Fish alerts Aquaman to an attack on Earth from an alien starfish named Starro the Conqueror. Starro has altered three ordinary starfish into his lieutenants. Aquaman alerts his friends Wonder Woman, Superman, Green Lantern, Batman, Flash, and J'onn J'onzz. Though Superman and Batman are too busy to attend, the rest meet and split up into teams.
The second starfish lieutenant steals a laboratory filled with a braintrust of scientists with the intent of absorbing their knowledge of earth science and defenses. Working to free the scientists, Wonder Woman and J'onn J'onzz discover that Starro's lieutenants can transfer absorbed power and knowledge to the others, as this Starro can now fire nuclear blasts.
Flash faces his Starro duplicate in Happy Harbor where the entire populace have fallen under Starro's influence, except for one lone teenager. Flash defeats the third Starro lieutenant, learns where the real Starro is, and decides to let "Snapper" Carr join him for the showdown.
Justice League of America [Wonder Woman [Diana Prince]; Green Lantern [Hal Jordan]; Aquaman [Arthur Curry]; Martian Manhunter [J'onn J'onzz]; Flash [Barry Allen]; Batman [Bruce Wayne] (cameo); Superman [Clark Kent] (cameo); Snapper Carr (joins)]; Starro (villain)
During the final battle, Flash and Green Lantern determine that Snapper is covered with lime, and that prevents Starro from affecting him. A few barrels of lime, and Starro becomes a souvenir for the JLA trophy room.