Huey, Dewey and Louie are on their way over to Gyro's house to have him repair a painting machine that he invented. When the boys arrive, they see that there is a long line up of customers waiting for Gyro to fix their machines. Gyro has had a long day, and the last thing he wants to do make more repairs. After Gyro gets chewed out for not being able to fix Vacation Van Honk's automatic dressing machine, a sweet, female duck asks him to fix her toaster. Gyro's attempt to fix the toaster only makes things worse, and the woman huffs off in disgrace. As for Gyro, he has gotten really frustrated by this point, feeling that everyone in town only looks at him as nothing more than a gadget man. Feeling sorry for Gyro, the boys decide to not ask him for his help. Instead, Gyro gets the idea that in another time, people would've appreciated him more.
The next day, the boys return to Gyro's house, and see a flash of light flare out from the windows. When they enter, they see that Gyro has just finished building a time machine out of an old bathtub, which he calls the Sometime Tub. Gyro declares that he'll go back to a time when he would've been something more important, and decides to become a knight. Dewey suggests that Gyro bring his tools with him, but the last thing Gyro wants is to be associated as a gadget man, even in the past. After casing a small mess, Gyro activates the Sometime Tub, with the boys inside, and the four of them travel back in time to the Middle Ages.
When they arrive in the middle ages, they see a king, and his magician, Moorloon, riding away from a black knight on horseback. Moorloon (who speaks in a German accent,) tries to stop the knight with magic, but he fails. Gyro rigs up a slingshot from an old tire and a mop that was in the Sometime Tub, and uses it to scare off the knight. The king and Moorloon meet up with Gyro and the boys, and welcome them to the land of Quackelot. Huey asks if the king is King Arthur, but the king corrects him, stating that he is not the dull King Arthur, but rather, King Artie, who loves to party. Gyro introduces himself as Sir Gyro de Gearloose, and is asked back to Artie's castle to attend a party.
Meanwhile, at another castle, the black knight (who is actually a scrawny goose hiding beneath thick armor), is being scolded by Lessdred, King Artie's evil nephew, for failing to eliminate the king. After whining about King Artie a bit, Lessdred comes up with an idea. Lessdred sends the black knight to a dragon's cave to throw rocks at the sleeping dragon within in the name of King Artie. The dragon wakes up, furious, and attacks the knight with his fire breath.
Back at King Artie's castle, there is a dinner party going on, where Gyro is the guest of honor. Everyone is impressed with Gyro's contraption from before, except for Moorloon, who feels that his magic is better. When Moorloon tries to impress everyone by summoning a thunderstorm, King Artie tells him to keep down the lightning storm. Gyro impresses the people by demonstrating how a magnet works, but he would rather talk about knight-related topics.
The dinner is interrupted by the dragon, who is trying to burn down the castle. When Moorloon claims that he can't take care of dragons, Gyro ends up rigging up a device that sprays cider, which he uses to put out the dragon's breath. Unable to blast more fire, the dragon flies off in a drunken manner. Moorloon is upset over Gyro's victory, while King Artie congratulates him.
Gyro then rejects Artie's request to build a machine that can create party hats, and decides to become a knight. His first attempt to practice jousting doesn't go over very well, but he eventually gets the hang of it. When Huey asks Gyro about returning to the present, Gyro tells them that he'd rather stay a knight in Quackelot instead.
That night, in their room in the castle, the boys, although they could go back in the Sometime Tub, choose to stay with Gyro instead. When they hear Moorloon walking by their room, the boys investigate, and follow him all the way to Lessdred's castle, where they spy on him. Moorloon then makes a proposition for Lessdred, in that Lessdred will sneak into King Artie's castle by use of a secret entrance and seize Gyro. The boys attempt to escape from the castle, but get caught by the black knight, who locks them in chains in the dungeon. Soon Moorloon gets tossed (literally) into the dungeon as well. Because Moorloon already told Lessdred about the secret entrance to King Artie's castle, Lessdred chose to betray him, and prepares a siege to overthrow the king.
Moorloon, who's ashamed of himself, admits to the boys that he just wanted to get rid of Gyro. Louie tells Moorloon that he doesn't need gadgets if he has magic instead. Moorloon whines about how people take his magic for granted, while Dewey tells him that people always took Gyro's gadgets for granted.
Back at King Artie's castle, King Artie is awakened by Lessdred's army, who enter the castle through the secret entrance. Artie and Gyro attempt to fight them off, but are unsuccessful in doing so. Lessdred then has Artie taken prisoner.
Meanwhile, the boys convince Moorloon that he should just stick to magic, which is what he's good at, and not to worry about inventions. Moorloon then remembers about how King Artie is in danger, and the boys offer to help. Moorloon uses magic to free the boys from their chains, and trick some guards into opening the door so that Moorloon can turn the guards into newts.
The boys and Moorloon head back to Artie's castle, where the siege is still going on, and meet up with Gyro, who's fallen in the grass. Gyro is upset over how he failed, but Moorloon tells him that a gadget man is just the kind of man they could use at this point. Gyro then gets an idea when his magnet gets stuck to his own armor.
After the siege, Lessdred has overtaken Artie's throne, and crowns himself the new king. When he and the black knight hear something from outside, they look out the window, and see a huge ball of chains (actually a magnet) being wheeled to the castle in a wagon. Lessdred sends for his knights to stop them. Moorloon then summons a thunderstorm, and the magnet gets charged up when it gets hit by a lightning bolt. Gyro then activates the charged magnet, which attracts all the enemy knights towards it. When Gyro, the boys and Moorloon return to rescue Artie, they learn that Lessdred and the black knight are stuck to the ceiling, as the powerful magnet is still activated.
The next day, Gyro and the boys prepare to return to the present. King Arthur questions why they have to leave, but Gyro reminds them that they don't need his gadgets as long as Moorloon has his magic. Gyro and the boys then return to the present, where Gyro is thrilled to be back home with his gadgets again. Just then, the woman with the toaster from before shows up, apologizes for her attitude earlier, and presents Gyro with a bouquet. Gyro announces that he wouldn't have it any other way.