In Metropolis, the Parasite fights Metamorpho and Elongated Man, draining their energies. He turns to find Batman facing him and the villain easily absorbs the explosion of a batarang. The Parasite then attacks using the Leaguers' stolen powers and Batman calls J'onn for reinforcements.
A plane goes down above Metropolis and Superman lowers it to safety. J'onn contacts him and Superman says that he needs 30 seconds, but a figure superspeeds by him. By the time Superman arrives, he discovers that new member Captain Marvel has finished off Parasite. They introduce Captain Marvel to Superman, who was on a mission when he joined the team. Captain Marvel is overwhelmed and Superman assures him that it's a pleasure.
As the Metropolis police take Parasite away, the press arrives to interview the League's newest member. Lois Lane is there and gets a statement, and Captain Marvel is full of admiration for the League, saying that they change the world. He points out that Lex Luthor used to be a villain and now he's running for President. Captain Marvel flies back to his hometown of Fawcett City, arrives at his elementary school, and transforms into his alter ego of Billy Batson and arrives late for class. The teacher tells him to take some responsibility and grow up.
Later, Captain Marvel goes to the Watchtower and greets his new teammates. Superman ushers him to the main meeting hall where the core members have assembled. They point out that he is quoted as endorsing Luthor as President and Superman points out that when he joined the League, he gave up being just a hero. Superman angrily says that they don’t super-villains and Captain Marvel insists that he simply said that Luthor had changed. When Superman says that things aren't that simple, Captain Marvel disagrees. The League tells him not to make any more public statements without League approval and Captain Marvel walks out.
Lex is on a news show talking about his newest project, Lexor City. Superman watches as Luthor talks about how it's a new start for low-income families. Captain Marvel comes in as Luthor points out that Hawkgirl was once a traitor but has been welcomed into the League. Luthor mentions Captain Marvel's statement and assures the host that he plans to take advantage of the chance for redemption. He then announces a charity open house the next night and extends an open invitation to Superman.
The next day, Superman and Batman are fighting the Cadre and discussing Superman's attitude toward Captain Marvel. Batman jokingly admits that he's sunny, which is why they're defending. Once the villains are defeated, Professor Hamilton calls Superman and invites him to his lab. He explains that robbers broke in and took four pounds of weapons-grade kryptonite. Batman confirms the lock was picked with LuthorCorp technology, but admits that anyone could have gotten hold of the equipment or used it deliberately to frame Luthor. Superman doesn't believe it and figures Luthor wants him to know, but Batman isn't convinced. He goes to Watchtower to consult with the Atom and tells Superman to go to the charity event and keep an eye on Luthor.
That night at Lexor City, Luthor introduces the children that will be moving in as Superman looks on. As the children hit the buffet line and the playground, Billy Batson watches from the shadows. Luthor all but breaks into tears as a disgusted Lois looks on. He then thanks Superman for his help and offers toast to the hero. Luthor's assistant Mercy calls him off to the side and Superman listens in as she tells her boss that the device is in place and ready to go off in six minutes. The hero scans the area with his x-ray vision and finds an underground complex beneath the playground and a bomb. Superman tells everyone to clear the area and the crowd panics.
Billy ducks off and transforms into Captain Marvel while Superman begins ripping the playground apart. Luthor tries to tell him that he doesn't understand but Superman brushes him aside. Captain Marvel flies in and Luthor appeals to him, explaining that he has placed an experimental kryptonite fusion reactor to power the city. Superman doesn't believe him and Luthor admits that he thought Superman wouldn't believe him. Captain Marvel suggests that they call in a technical expert to examine the device, but Superman warns that there isn't enough time and shoves them both aside.
Captain Marvel tries to stop Superman and the Kryptonian shoves him and Luthor away. While Luthor pleads with them to resolve their difference peacefully, Captain Marvel throws Superman into the sky and then flies after him. The two heroes clash in mid-air and are knocked back, demolishing the nearby buildings. Captain Marvel returns to the attack but Superman pummels him back through the buildings. The two heroes continue to exchange blows, destroying everything around them.
Superman finally stuns Captain Marvel and then drills down to the bomb. However, a battered Captain Marvel comes at him again, grabs Superman, and repeatedly says his magic word, Shazam! The mystic lightning strikes Superman twice, injuring him, but he then grabs Captain Marvel and lets the lightning hit him instead. He's transformed back into Billy Batson and Superman gags him before he can speak again.
With seconds left, Superman melts the bomb down with his heat vision. However, later, the Atom confirms that the "bomb" is exactly what Superman said it was. Superman apologizes as the press snaps pictures, and Luthor says that he should have known better than to make it a surprise. The Man of Steel assures everyone that the League will pay for the damage, but Luthor tells the press that he'll take care of it.
Back aboard Watchtower, Captain Marvel calls a meeting of the founding members. Superman tries to apologize but Captain Marvel insists on having his say. He tells them that he's always believed in fair play but they don’t anymore, and that he's quitting the Justice League. Once he leaves, Superman admits that he's right. Batman points out that "they" set him up.
At his office, Luthor tells his conspirator, Amanda Waller, that his plan went better than he thought since Superman demolished Lexor City in front of the press. Together the two of them share a toast to their success... and things are just getting started.