Batman and Wonder Woman are flying to Superman’s Arctic Fortress of Solitude to give him presents on his birthday. They enter the cavern and discover Superman standing immobile, with a violet plant attached to his body.
They quickly determine that Superman is still breathing and conclude someone breached the Fortress. Wonder Woman goes to search while Batman determines that Superman is totally cut off from any sensation.
In his dream world, Superman wakes up on his farm on the planet Krypton on his birthday. Superman’s wife, reporter Loana, wakes up next to him. There’s a brief rumbling noise but Loana doesn’t seem to notice it. Their robot servant Brainiac comes in to inform them that Kal-El and his son Van-El is expected at Jor-El’s laboratory.
Batman concludes that an alien planet sent the container as a gift, but it was a ruse. A voice comes out of the shadows, congratulating him on his deductive abilities. Mongul steps out of the shadows, holding the unconscious Wonder Woman. As Mongul boasts, Wonder Woman wakes up and kicks him. but Batman interrupts their battle. Mongul obliges by explaining that the plant, the Black Mercy, latches on to a victim and feeds them their heart’s desire. Furious, Wonder Woman attacks Mongul, hurting her hands in the process. Mongul is unimpressed and notes that Superman was the only obstacle to his plans.
Kal-El is making breakfast and insists that his son Van-El clean up after himself. Van-El comes down along with his pet dog Krypto. Kal-El quickly forgives him but Van-El lets slip that there’s a surprise party for his father. Loana assures him he’s not getting one and tells them to eat their breakfast so they can meet with Jor-El. Kal-El insists he doesn’t want a surprise party and Loana convinces him to go along with it.
Batman tries to distract Mongul while Wonder Woman keeps the alien conqueror off-balance. Batman, realizing his efforts are useless, tries to burn off the Black Mercy with a laser but with no success. Batman tries to get through to Superman, telling him to shake it off. Meanwhile, Mongul knocks Wonder Woman into Superman’s arsenal. She fires a neuro-impactor at him but he shrugs it off. Batman is unable to find anything that will remove the plant and tries to get through to Superman.
Kal-El and Van-El arrive at Jor-El’s laboratory and Van-El is surprised that his father left everything to work on a farm. The planet shakes again and Kal-El confirms with Brainiac that it is a harmless tremor predicted weeks earlier.
Mongul grabs Wonder Woman and starts to throttle her. He slams her into the ground and then kicks her in the head.
In Jor-El’s laboratory, Kal-El notices a Black Mercy plant in a container. Jor-El asks him what’s wrong and Kal-El points out there are a series of tremor that indicate something is wrong. Jor-El talks about how he once announced Krypton was going to explode but he was wrong. Kal-El has second thoughts and Jor-El tells him to focus on the future. As they go up on the roof to look at Jor-El’s macroscope, Kal-El briefly hears the voice of Pa Kent but no one seems to notice. Kal-El insists that something is wrong, and starts to come out of his trance in the real world. In the dream world, Kal-El hears Batman’s voice and turns to Van-El. Kal-El tells his son that his birth was the greatest day in his life, but he realizes nothing there is real. Kal-El tells his son he has to go now as the entire planet is swallowed up in eruptions. Superman promises that he’ll never forget him.
Batman pulls the Black Mercy loose.. and it attaches itself to him. Batman finds himself reliving his childhood where his parents didn’t die. Thomas Wayne defeats the robber, and in the real world Batman smiles in happiness. Superman wakes up and slams into Mongul at superspeed, knocking him into the intergalactic zoo. As the two battles, a badly injured Wonder Woman crawls across the floor to Batman. Realizing the Black Mercy has ensnared him, she pulls it loose while in the dream world, young Bruce cheers his father on. He hears Wonder Woman calling to him and realizes what’s happened. Wonder Woman pulls the Black Mercy free and wrestles with it as it tries to attach itself to her.
Mongul gets the upper hand against Superman and smashes him down into the next level. Superman smashes into him without mercy, but looks up to see the statue of his parents. He hesitates and Mongul knocks him down and moves in for the kill. However, Wonder Woman arrives and tosses the Black Mercy onto him. The heroes look at the immobile Mongul as Wonder Woman gives Superman her gift: a new breed of Amazon rose. Superman considers the statue of his parents and promises he’ll never forget. The heroes wonder what Mongul is seeing in his dream, but Batman notes that whatever it is, it’s too good for him.