In an untold Batman story, the Egyptian super villain Pharaoh uses a mystic scepter to transform humans into obedient zombies. He unleashes them on a bank, transforming the guards who try to stop them. As Pharaoh exits to his Sarcophogusmobile, photojournalist Vicki Vale arrives to take photos, and witness the arrival of Batman and Robin... wearing mummy wrapping. The Pharaoh unleashes the power of the scepter on them, but Batman reveals that they have soaked the wrappings in buttermilk, the only thing proof against pharaoh rays. The heroes quickly subdue the zombies, knock the Pharaoh out, and break the scepter, returning the zombies to normal.
In Metropolis, Jimmy Olsen pretends to be sick so he can get the scoop of the century and hoax Superman into revealing his secret identity as Jimmy's dying wish. Superman comes to his pal's side but quickly realizes that Jimmy is trying to trick him. He leaves to deal with an emergency: a robbery at a museum. Batman is there and explains that he's been following a jewel thief up the Eastern Seacoast. Lex Luthor emerges from the museum in a flying vehicle, and reveals that he has Lois Lane hostage. Refusing to play the damsel in distress, Lois kicks a lever and the vehicle goes out of control. Much to her surprise, it is Batman that rescues her while Superman quickly subdues Luthor. Superman then invites Batman to take a break from Gotham City and help him in Metropolis for a while, and Batman agrees.
At the Daily Planet
, editor-in-chief Perry White assigns Lois and Jimmy to write a "Day in the Life of Superman" story. Lois writes of how Superman protects Metropolis, with an assist from Batman, against super villains Metallo and Mr. Mxyzptlk. Lois concludes her story and is surprised to receive a red jewel necklace from a secret admirer, who she assumes is Superman. Jimmy receives a new signal watch made of the same substance.
The Toyman launches an attack on Metropolis, and Lois and Jimmy go to the bank to get the story. They watch as Superman first defeats the deadly toy sand then captures the Toyman, and then approach their friend. Once they get close, Superman suddenly transforms, sneering and saying that he's had enough of super villains attacking Metropolis. He brutally throws the Toyman down the street and prepares to kill him, but Batman gets the villain to safety just in time. Superman tells them to stay out of his way or he'll kill them the next time they meet, and flies away as Batman and the others realize that something is wrong with the Man of Steel.
Superman goes on a rampage of super proportions, blotting out the sun with thunderclouds, twisting Metropolis' main bridge into a pretzel, and putting a cat into a tree. Perry White has Lois and Jimmy do a story on this new, evil Superman. Batman checks in on the two reporters and confirms that they both received red jewel gifts at the same time, right before Superman turned evil. Batman goes to the Fortress of Solitude and finds Superman terrorizing the residents of the bottle city of Kandor, while the superdog Krypto looks on at its master. Superman confirms that he didn't give the gifts to his former friends, and orders Batman and Krypto to leave. They go to the Batcave and check the red jewel material, and Batman confirms that it's red kryptonite, which causes Superman to transform in unpredictable ways and lasts for 24 hours.
Next, Superman captures the mayor of Metropolis and declares himself king of the city. He demands tribute but Lois and Jimmy lead an uprising, only to be quickly blown away in a blast of super-breath. Batman arrives, wearing a battlesuit, and dares Superman to attack him and Krypto. Despite the advanced technology, the battlesuit proves no match for Superman's strength and invulnerability. Krypto provides a brief respite, and working with Batman, try to delay Superman until 24 hours elapse and the red kryptonite wears off. Superman smashes open the strength, causing Jimmy and Lois to fall into the resulting crevasse. Jimmy holds onto the edge, and Lois holds onto Jimmy, until Krypto can rescue them. Meanwhile, Superman grabs Batman's helmet and prepares to crush it. Batman asks him what Ma Kent would think of her adopted son turning evil, and Superman grows even angrier... just as the 24 hours are up and the red kryptonite wears off. Relieved, Superman apologizes for his actions, and he and Batman both realize there is only one other person who knows about red kryptonite.
Luthor is watching the battle from his observatory when Batman and Superman smash through the wall, with Lois and Jimmy there to cover the story. The villain boasts that they merely captured a Lexbot and sent it to prison, and that he has engineered the entire thing to discredit Superman in the eyes of Metropolis' citizens. He shoots Batman down with an electro-ray and then uses a green kryptonite ring against Superman. Superman hesitates, starts to crumple, and then... stands up, smiling. He knocks Luthor down and then reveals that he's a disguised Batman. "Batman" gets up and removes his mask, revealing that he's Superman.
Later, the citizens of Metropolis throw a parade for the two heroes, Luthor's plan to discredit Superman has failed, but Lois is disappointed that Clark Kent scooped her on another story. She gets Superman to promise to cheer her up by taking her on a dinner date. However, their plans are interrupted when a new villain arrives in town: Brainiac, who prepares to shrink Metropolis. Together, Batman and Superman team up to take on the villain.