High above the planet Earth, the evil Black Adam enters the atmosphere in a fiery blaze! While at the mansion, Billy and Mary are looking through a telescope and Billy thinks for sure he saw something. (And he did, it was Black Adam that he saw). But Mary isn't convinced he saw anything and that his eyes must be playing tricks on him. She tells him he's not seeing a U.F.O., he's only seeing someone's kite. Just then Freddy Freeman tells them not to hog the telescope. Freddy says he wants to go next, but Mary said it at the same time. So Freddy says "Let's flip a coin." Just then, Uncle Dudley walks into the room and tells them to let an expert handle this. Billy asks him if he is an expert on U.F.O.s, and Dudley says "Am I ever?!" He then takes a look through the telescope and he beholds Black Adam coming. Billy says they better take care of the situation as the Marvel Family. Mary and Billy utter the magic word "Shazam!" And they transform into Mary Marvel and Captain Marvel. Freddy utters the name of his favorite superhero, which is the magic word that transforms him into Captain Marvel, Jr. The three of them then fly out the window and Uncle Dudley tells them "Wait for me!"
Meanwhile, in downtown Fawcett City, Black Adam is flying over the city, and the citizens of Fawcett City are in a state of panic. Black Adam flies passed the WIZZ-TV building, and lands in a street next to Furs. He says that he knows that he's getting nearer, and that the Princess is somewhere nearby. Just then, a man in a car honks his horn since he is standing right in the middle of the road. Black Adam angrily lifts up the automobile. Meanwhile, in the sky, Captain Marvel observes the situation below from above. He flies down and grabs the car and sets it down safely. Just then, Mary Marvel and Captain Marvel, Jr. land next to Black Adam. Captain Marvel tells him he could have hurt that man, and Black Adam tells him he does as he pleases! He then lifts a street lamp from the ground and prepares to strike Captain Marvel with it. Captain Marvel tells him that it's public property and he better put it down, he grabs it, and plants it back into the concrete. Black Adam is marveled that he seems to be as strong as he is. Just then, Uncle Marvel finally catches up with the others, and says "Almost! But what makes you think you're a match for the Marvels!" Black Adam then asks Uncle Marvel "Are you a Marvel?" Then he grabs him and throws him up into the air, and Uncle Marvel grabs hold of a pole on the side of a building. Captain Marvel and Mary Marvel take to flight and rescue him. Meanwhile, on the ground, Captain Marvel, Jr. faces off against Black Adam. He asks him "Where do you think you're going?" To which Black Adam responds "Nowhere that concerns you!" Black Adam throws some kind of magic dust pellet at Captain Marvel, Jr. and he is transformed, and he now has a dog face with what appears to be some sort of Egyptian turban on his head. When Captain Marvel and Mary Marvel return to the ground they find that Black Adam is gone and Captain Marvel has been transformed. Captain Marvel tells them they need to get to the wizard's cave.
At the Rock of Eternity, Captain Marvel says that the only thing that can cure Captain Marvel, Jr. is magic, so they summon the spirit of the deceased wizard Shazam. He appears in the form of a ghost, and tells them he had been expecting them, because he sensed an evil so great that it could only mean that Black Adam has returned. Captain Marvel, Jr. howls as if in fear over what he had just heard. Using his magic, he transforms Captain Marvel, Jr. back to his normal, former self. Captain Marvel then asks the wizard who Black Adam is, and how he's so powerful. The wizard then tells him that 5,000 years ago, he gave the Egyptian Teth-Adam the same power he gave the Marvel Family, but he became evil. He had banished him at the End of the Universe, but now, 5,000 years later, he has returned. Captain Marvel asks him what he is planning. Shazam tells him that he is going to claim Princess Jemi as his bride. The Marvels ask how they can defeat him when he has all of their powers and the magic of Ancient Egypt. The wizard tells them there's only one way to defeat Black Adam. When they ask him how, he tells them he cannot answer, but he's confident they will be able to stop him. Baffled, Captain Marvel, Jr. asks where they should start. Captain Marvel says that the name Princess Jemi sounds familiar. Dudley mentions that he seems to remember Mr. Tawny mentioning the name relating to a mummy in an Egyptian exhibit at his museum. Captain Marvel tells him the mummy is the mummy of Princess Jemi. They immediately disembark.
Later, at the museum, the kids are now back to their normal non-superhero selves, and they are looking around in the museum, wondering where the mummy of Princess Jemi is. Mr. Tawny walks toward them, and Billy says that he'll be able to tell them where it is. Mr. Tawny tells them he's glad they showed up, because there's a weirdo in the Egyptian exhibit. Immediately they are certain it must be Black Adam. So they head inside the Egyptian exhibit to see what he's up to, and in the Egyptian exhibit, he is casting some sort of magic spell to awaken Jemi. She smashes the door of her pyramid tomb, and emerges with no sign of decay from her 5,000 year death whatsoever. She says she's free at last, and she asks what took him so long. He tells her it was the wizard who sent him to the end of the universe before he could set her free. She tells him she's not interested in his excuses. She then asks him "Do you know what it's like to be wrapped up like a sack of potatoes for 5,000 years!" He tells her she's free now. She then says "I suppose so." But she then tells him she won't put up with anymore of his bumbling. Elsewhere in the room, the Marvel Family and Tawny are hiding behind one of the Egyptian artifacts in the exhibit, and observe how Jemi is really laying it into Black Adam. Jemi tells Black Adam "Come on, let's go." Black Adam looks terrified. Mary is surprised to see that Black Adam is so afraid of her. She then makes the statement, that if she's more evil than he is, they are in for some big trouble. Black Adam then kneels down and kisses Jemi's hand and arm and tells him he's been waiting years for this. Just then, the Staff of Osiris starts to glow, and Tawny says he never seen it do that before. Billy deduces that it must have something to do with the Princess. Black Adam tells Jemi that before they depart they should leave a mark for them to be remembered by, he walks up to an artifact and yells, "Arise Thoth!" And the statue came to life. Then, Jemi walks up to a crocodile statue, and shouts "Awaken Sobek! And the crocodile comes to life. The two monstrous deities crash through the wall and exit the museum. Black Adam then tells his princess that with the Marvels after them, they'll have something to keep them busy. The two then fly up into the air and smash through the ceiling and crash through the roof of the building. Tawny asks "Aren't you going after them." But they realize that they'll have to stop the monsters first, because they are on a rampage in Fawcett City. They then change to the Marvels with their own magic words and race after the monsters, but before they leave, Tawny tells them to take the Staff of Osiris, because it may help defeat them since it has magical powers. They then go after them.
At sea, they find the crocodile. Mary says she'll take care of him, and Captain Marvel says they'll take care of the baboon. She spots the croc trying to catch a cruise ship, and so she grabs him by the tail, and then throws him into outer space. Meanwhile, elsewhere, Captain Marvel and Captain Marvel, Jr. go locate Thoth. Captain Marvel says they might be able to use the magic of the Staff to stop him. The beast, standing in front of Smith's Bakery, faces off against them ferociously. Captain Marvel, Jr. grabs the beast by the foot and knocks him down in the street right in front of the Spears Drugs store. Captain Marvel then uses the magic of the staff to make the monster shrink and then vanish into thin air. Mary catches up and says that takes care of the creatures, but what about Black Adam? Captain Marvel commands the staff to take them to Black Adam. And so it pulls the three of them to Egypt, where they see the Pyramids and the Great Sphinx of Giza. They are drawn to the entrance of one of the pyramids...and they stealthily enter. Inside, Black Adam is engaged in some sort of magical spell. He tells Jemi that the people of earth will soon become their slaves. But Captain Marvel makes his presence known and tells him he has other things in mind. Jemi sees that he possesses the staff and she tells Black Adam to grab it from him. He reaches out to grab it from him, and the two struggle with the staff. Captain Marvel shoves Black Adam to the ground, and the staff goes soaring through the air, and lands in a pit of fire that Black Adam was using for his magic spell. The staff is destroyed, and so it's magic is reversed and so Jemi vanishes in a puff of smoke, returning to the grave. Black Adam is angered, and he says "By the power of Anubis, hault!" And then the Marvels stop in their tracks as if frozen. He tells them he warned them. He walks up to Mary and lustfully caresses her face and notices that she is much prettier than Jemi and decides that she would make a worthy Queen. He then hypnotizes her into agreeing with him...and the other two Marvels are shocked by what's going on, and unable to move. He then blasts rays from his eyes that freeze them. And he flies off with Mary, crashing through the roof of the pyramid. But the sunlight beams down on the ice and quickly melts it, allowing Captain Marvel to easily break through the melting ice, and then with a super punch with his super strength, he smashes Captain Marvel, Jr.'s icy prison as well. Junior says he may never look at an ice cube again. Then Captain Marvel tells him they have to hurry before Mary is lost to them forever. They then fly out of the roof of the museum.
Later, in outer space, Captain Marvel and Captain Marvel, Jr. are heading after Black Adam so that they can save Mary. Captain Marvel, Jr. asks Captain Marvel how they can stop him even if they do catch him. And what's the secret method of defeating Black Adam that Shazam wouldn't tell them. Just then Captain Marvel says "That's it! That word...we just have to get Black Adam to say the magic word!" Captain Marvel is confused, wondering what that would accomplish. Then Captain Marvel told him he'll see when it happens. He tells him they'll need to find some wood. So he flies down to the surface of an alien planet and starts knocking down trees, and Junior catches them, collecting the wood.
Elsewhere, in outer space, Black Adam and Mary Marvel are flying toward an unknown destination. Black Adam tells her that they will soon arrive on his planet. She responds "Yes master." And he asks her if she's all right, and she responds "I don't know, master." She then goes on to explain to him that she thinks she senses that someone is watching her. He tells her it must be her imagination but she informs him that she is almost sure. He tells her that it's nonsense, and then he tells her to "Think of something cheerful like beating the slaves while they build the pyramids." They then notice a strange sight in their path, a giant green treasure chest unmoving in space. Black Adam tells her "Let's go have a look at it." So they fly down and land on the strange object. He looks inside the chest to find out if anything's in it. Meanwhile, nearby, Captain Marvel and Captain Marvel, Jr. are hiding behind a meteoroid, hoping that Mary doesn't give their position away since she can sense them. While at the chest, Black Adam sees that the chest is indeed empty. But then he takes a closer look and notices an old scroll. He jumps inside the chest from the hole he made in it, and takes a look at it, thinking it to be a treasure map. Mary is still on top of the chest, and she notices Captain Marvel and Captain Marvel, Jr. behind the meteoroid, and she begins to tell her master that it's a trap, but he tells her to "Hush." He then proceeds to look at the scroll, then he begins to read the scroll, "To whom it may concern...Shazam." Instantly he turns to dust. And Mary is broken free from the spell. Captain Marvel explains that the minute that Black Adam said the magic word, he was automatically transformed back into his mortal form, and since his mortal form was over 5,000 years old, he was turned to dust, and when he turned to dust, Mary was freed from his spell. Mary then asks them what took them so long. The Junior says; "Let's go home. I'm actually looking forward to Uncle Dudley's cooking. They all then fly off, heading back for Earth.