The Justice League of America first appear with Wonder Woman, The Flash (Barry Allen), Aquaman, Green Lantern (Hal Jordan), and the Martian Manhunter teaming to spare the denizens of Happy Harbor, Rhode Island, from the mental thrall of Starro the Conqueror. Superman and Batman are revealed as fellow JLA members, although they do not aid in the adventure. "Young hipster" Lucas "Snapper" Carr is made an honorary member of the JLA and becomes the team's official "mascot". The Secret Sanctuary, a mountain cavern outside of Happy Harbor, is established as the League's first headquarters.
Upon its arrival to Earth, Starro enlists three "distant relatives" for planetary conquest. Aquaman is told of this plan by Peter the Puffer Fish and calls his fellow JLA members to stop Starro after seeing it as too big of a threat.
Due to there being multiple Starros, the League is forced to split up. The first Starro attacks a United States Air Force jet and sets off a nuclear bomb that it has stolen. Green Lantern survives the explosion by using his Green Power Ring to create a protective bubble around him and the Starro reverts back to a regular starfish.
The second Starro attacks the Hall of Science in Science City. It lifts up the Hall of Science and flies away with it. Wonder Woman and Martian Manhunter manage to defeat Starro and safely lower the Hall of Science to the ground.
At Happy Harbor the third Starro puts the entire townspeople into a trance (with the exception of Snapper Carr who was doing lawn work at the time). The Flash appears and begins pursuing Starro and is ultimately destroyed when the Flash collapses water on it.
With this, the Justice League of America and Snapper Carr rendezvous and discuss how to defeat the last and final Starro. After figuring out that the turf-building lime Snapper wore on his clothes made Starro's mental abilities ineffective, the League then confronts Starro and covers it in lime to defeat it. For his help Snapper is made an Honorary Member of the team.