Years ago, the martian J’onn J’onzz lived in peace with his wife and daughter before the ruthless conqueror Despero invaded the planet and killed them before his eyes. Before he could kill J’onn, however, he was miraculously transported to Earth by an invention of Dr. Erdel, who died of a heart attack upon seeing him. Heartbroken and alone, J’onn took the name John Jones and began a new life.
Years later, Despero sets his sights on Earth. Green Lantern Abin Sur confronts him but is killed, crashing on Earth and giving his ring to pilot Hal Jordan. With his new powers, Hal seeks out Superman, Batman, Wonder Woman, Flash, and Aquaman to form a team. Despero launches his invasion, using Starro drones to brainwash humanity.
The heroes meet John, who reveals his true identity and past. While they confront Despero aboard his ship, teenager Snapper Carr discovers how to stop the Starro drones, with help from Robin and Aqualad. Despero overwhelms the heroes with his telepathy until J’onn defeats him in a mental battle by overcoming his guilt.
Afterward, the heroes officially form the Justice League, while Snapper is honored for his role in saving humanity.
