The Doc works on a new invention, and when Derpy stops by for a visit, things go a little bit crazy.
While the Doctor is working on a new invention for the science fair coming up in Ponyville, confident to win, his good friend Derpy decides to pay a visit. She pulls the lever on the machine and it swaps their bodies! Now ponies think Doctor is Derpy, and Derpy is the Doctor. Can they resolve this issue before the judging starts?
Dr. Whooves was in his lab working out a few bugs on his project for the Science Fair. The machine was meant to swap bodies with anypony who stood near it. Unsure it would work, he had been adjusting some loose screws hanging on it. There was then a knock on his door.
"Yes?" he answered, but then saw it was a close friend, "Oh, why hello there, Derpy! Can I help you?"
The mare replied, "Hi, Doc! Oh, and yes, I wanted to know if you could help a filly. Her scooter just broke down outside your house."
It was Scootaloo, and she shouted from the distance, "Oh, come on! Stand up, you piece of junk!"
"Hmm. Perhaps I can help her out for a moment. I shall return, wait here. Allons-y!" he stepped out the front door and took a tool-box with him. While he was away, Derpy decided to step inside since it was getting humid out.
"Whoa...how does he make all this stuff?" Derpy asked herself as she walked around admiring all the gadgets. She saw the machine he had been working on before she came in, and marveled at it, almost touching the lever that controlled it.
Dr. Whooves ran in after helping Scootaloo before she got to it, "Wait! Do NOT touch that device!"
"Why? What's wrong with it?" Derpy questioned.
"Nothing, but great whickering stallions! Good thing you didn't pull that lever! You have no idea what you could have done." Doctor warned.
Derpy wasn't really paying attention since she was looking at his spare flameless fireworks, but responded, "Well, if nothing's wrong with it, can't I pull the--?"
"NO! It's too dangerous and still under testing, I'm not sure if it is ready to use." he anxiously exclaimed.
She sighed, "Okay...I'll just--" Derpy sat on the lever by accident.
"Wait, no!" he warned her too late, and they were both zapped by a neon-blue laser, switching their bodies and forms. "What just happened?" he took another look at himself, "M-My voice! Great whickering stallions! My invention works! IT WORKS!" he then gasped, "Wait a minute...I can't show up to the science fair like this! I can't even see where I'm going--oof!" he ran into a pole inside his lab.
Derpy laughed a bit, "You ran into a pole. Wait! My voice sounds weird, too!" she gasped, "I can see straight, too! Is this what your machine does?! Help ponies see better?!"
"No, no, no, not at all. It swaps anypony's body who is standing close by the device." he jolted, "Hang on, it switches voices and bodies...but not brains! I remember everything!"
"But why don't I like muffins anymore?" Derpy asked worried.
Dr. Whooves replied, "Really? You don't like muffins anymore? Hmm. Strange, I have a craving for muffins...great whickering stallions! Behaviors switch, too! This is a fonominole discovery! I may have a shot at winning the Ponyville Science Fair if I can switch our bodies back to normal. Come on, we don't have a lot of time to lose! Perhaps Princess Twilight can help."
"Okay." he was already out the door after Derpy replied, "Oh, wait for me!" she tried to fly, but forgot she had no wings. "Oh, shoot!" after realizing, she ran after behind him.
The Doctor had trouble getting there as well, his new wings were tempted to fly, and he couldn't seem to control them. "Blast! I want my hooves on the ground, you idiotic wings!"
"Hey, my wings aren't id-id...stupid!" Derpy protested.
Bon Bon looked over at them, then seemed to whisper to Lyra, "Gee, I thought all pegasus knew how to fly." they both snickered.
They both just ignored them, and kept carrying on to Twilight's castle. Finally, Derpy and Doctor had reached it. "Quickly, knock on the door! I can't see straight, or fly straight for that matter!" the Doctor exclaimed.
Derpy swiftly ran over and knocked on her door. "Princess Twilight, we need your help! Doc's machine wasn't working and, and..."
"Whoa, hold up, aren't you talking about yourself?" Twilight answered, looking surprised when opening the door.
"No, no! Our bodies are mixed up! You gotta help us!" Derpy pleaded.
Twilight looked back at Doctor, who still had trouble making his way to the door. "I see. I can also tell, because most pegasus can fly at this age."
He finally made his way over to explain, "Princess, our bodies have been switched, you need to aid us. I have a science fair to attend momentarily! You must fix my contraption!"
"B-But I don't know the first thing about machinery!" Twilight protested.
Derpy recalled, "But you made the portal in The Crystal Empire work again! You made that device to power the portal! Surely you could try to fix his machine!"
"Wait a second, how did you know about the portal? No pony is supposed to know about that!" Twilight shouted.
The Doctor stated, "Well. You certainly aren't doing a good job keeping your muzzle shut about 'it'." his wings began taking off again, but he managed to stay down to Earth.
"Princess Twilight, please, you need to help us. Doc has to win that competition!" Derpy pleaded once more.
The alicorn exhaled and replied, "I will try, but I can't promise anything. Alright?"
"Fair enough, your majesty." the Doctor said. So he didn't have to struggle again, Twilight used her magic to teleport them to his lab. "Ugh...I hate traveling by magic..."
"Do you or do you not want my assistance?" Twilight questioned.
He rolled his eyes, "Just come on, I want to get out of here!"
"Ahem." Derpy coughed.
Doctor chuckled nervously, "No offense, Derpy."
"None taken..." she responded coldly. On the inside, she didn't take it too hard.
Twilight used her magic to levitate a few tools. She listened as Doctor Whooves instructed her where to fix it. The machine had burst after being used, but it was being made stronger with every screw she tightened.
"And you just need to tighten up the last washer over there." Dr. Whooves finished off.
Twilight asked, "Okay, now what?"
"Pull the lever." he remarked. Twilight put a force-field around her to be sure she didn't hit herself, and then she pulled the lever. In almost an instant, Derpy and the Doctor's bodies were in the right place again. "Thank you, Twilight! Now, there's no time to waste...and I should know. We have to get to the science fair, now!"
"Not a problem." Twilight teleported them there, along with the machine in an open spot of the fair. "I'm also one of the judges, and you sure have my vote on this contraption!"
"Thank you, your highness! I hope I win, but if not, that's fine. For now, I think it's a better idea for you to enjoy the rest of the fair. I hear somepony brought radioactive animals." Dr. Whooves stated.
Derpy was confused, "...Somepony could really do that?"
"I don't see why it wouldn't be possible, but even so, it's just a rumor." the Doctor replied.
Princess Cadance was one of the judges, and as she walked by, the device caught her eye. "Hmm. Your invention seems very interesting, Doc. What exactly does it do?"
"This machine can switch anypony's bodies in the blink of an eye. Believe me, I've tested it. Derpy here was my...uh...'assistant'." Doctor Whooves shakily said.
"Hmm...well, you've got my vote! Good luck winning the fair!" Princess Cadance smiled and checked her board, then walked away to another project.
Not long after, Princess Celestia was up on stage at the front of the fair, "Everypony, the time has come to announce the winner of this year's Ponyville Science Fair! Now, even though you may not have been the one to win, just know that we've all seen some pretty fascinating inventions and it was a tough choice. However, we can only have one winner here, and the Inventor's Trophy goes to...Dr. Whooves!" cheers roared over a crowd of inventors, and many ponies congratulated Dr. Whooves.
"Wow! You won, Doc! Congratulations!" Derpy smiled.
"Thank you, Derpy. Even though you sort of messed with my machine, I don't think I could have won this without you." he remarked. He gave her the trophy instead. Derpy smiled once more, and then after the fair, they both went home and were ready to start another day.
