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 on Earth, Starro enlisted three starfish "distant relatives" for planetary conquest. Aquaman in told of the plan by Peter the Puffer Fish. Seeing Starro as a too big of a threat he calls the Justice League of America together.
As there are multiple Starros the team is forced to slip up to deal with the threat. The first Starro attacks an United States Air Force jet and steals a nuclear bomb. Starro explodes the bomb and Green Lantern is able to survive by using his power ring to make a bubble around him. After the explosion Green Lantern the Starro copy is reverted to a regular starfish.
The next Starro attacks the Hall of Science in Science City. It actually lifts up the Hall od Science and flys away with it. Wonder Woman and Martian Manhunter are able to defeat Starro and lower the Hall of Science safely to the ground.
At Happy Harbor the third Starro put the whole town in a trance with the exception of Snapper Carr who was doing lawn work at the time. The Flash shows up and chaces down Starro and defeats him by crashing water down on it and destrying it.
With this the Justice League of America and Snapper Carr meets and discusses how to defeat the last Starro. They confront Starro when they figure out the turf-builder lime that Snapper was using made him invulnerable. Using more lime they defeat Starro. For his help Snapper is made an Honorary Member of the team.