At Skips' house, (Y/n), Mordecai and Rigby are cleaning out his garage while he's on the phone. "Sorry Gary, I can't. I'm cleaning out my garage today." Gary and the Guardians of Eternal Youth are traveling the galaxy in Gary's El Camino. "But we haven't had a guy's night out in ages and we're passing right through your galaxy." Gary said. "I told you, I can't go!" Mordecai grabs a hat rack and notices something. "Whoa! (Y/n), Rigby get over here." He said. "Let me guess, immortal  junk... Whoa." They are looking at a synthesizer. "Dude, that's the coolest thing I've ever seen." (Y/n) said. Rigby walks up to it, mesmerized. "So cool." He said. "No, dude! Look!" (Y/n) points to the sign that says "Do not touch" Rigby scoffs. "How many times does touching stuff we're not supposed to caused a problem?" He asked.

"Like every time, dude." (Y/n) crosses her arms. "Well, maybe this time nothing will happen. Watch." Rigby cranks up the volume. "Cool." Mordecai and Rigby said. "Guys, I really don't think we should be-" (Y/n) began. Rigby pulls out a plug, which causes a small surge as the synthesizer vibrates. "Nice. Hmm."

Rigby puts the plug in a different outlet. "Yes yes yes!" Mordecai said. They both giggle as they start mixing the plugs around, and (Y/n) grabs Rigby's right arm. "Boys, stop it!" She scolded. Skips enters the garage. "What are you doing!? That's Gary's synthesizer!" A crash is heard. The four of them look outside to find the Guardians of Eternal Youth dazed as they exit Gary's El Camino, which crashed into a tree. "Are you guys okay?" (Y/n), Mordecai, Rigby and Skips head over to them. "We're fine." Reginald said.

"Where's Gary?" Skips asked. "Well," there's a flashback to when they were traveling. "We were on our way to the galactic mall..." "Come on, Skips." Gary said. "...when Gary straight up disappeared." Gary disappears, causing the Guardians to gasp. Boswold grabs the steering wheel. "I don't know how to drive the stick." They all scream as the car swerves. "Only one thing could've caused this.

Reginald said. "Which one of you messed with his synthesizer?" Boswold asked, and Skips and (Y/n) glare at Mordecai and Rigby. "Uh, messed with?" Rigby asked. "I mean, we might've unplugged some cables." Mordecai said. "Fools! That device synthesizes Gary's physical being into existence." Reginald scolded. "So, Gary's dead?" (Y/n) asked worriedly. "No! His consciousness still resides within the snyth. But, until you put the cables back to make the correct patch, the device won't project his physical form." Reginald said.

"It's cool. We'll just put it back the way it was. How hard can it be?" Rigby asked. Everyone is gathered at Gary's synthesizer. "Skips?" Mordecai asked. "Oh, no no. Can't help you here. Just plug back the cables you unplugged." Skips said. "Right."  Mordecai said nervously. "Piece of cake." Rigby said. The two of them plug the cables into random spots. "Hm, hm, hm, hm, hm!" The duo said. Rigby presses a key, which causes the synthesizer to emit a loud high frequency sound. This culminates in Skips' windows and his glass harmonica shatters. "My priceless glass harmonica!" Skips shouted. (Y/n),

Skips and the Eternal Youth Guardians glare at Mordecai and Rigby. "Any sign of Gary? No?" Rigby asked. "Why would Gary leave such an important thing in Skips' garage?" Mordecai asked. "Hmm... good question. You'd think with something as important as this he'd want to keep it hidden or something..." (Y/n) mused. "That's it! You must travel to Gary's home world of Synthos to recreate the synth patch to bring him back!" Reginald said. "Wait, what?" Reginald snaps his fingers, transporting (Y/n), Mordecai, Rigby, Skips, and Gary's synthesizer to Synthos. "Aah!"  Mordecai and Rigby shouted. At Synthos, the four of them and the synthesizer, which Mordecai and Rigby are carrying, arrive. "Whoa." (Y/n), Mordecai and Rigby said.

David and two of his guards appear. "Welcome, new arrivals, to Synth City. I'm David, King and Ruler of Synthos." He said. " 'Sup? I'm Rigby. I'm the King of Earth." (Y/n) hits him with the synthesizer. "Oh! Ow." He said. "Welcome, Earth ambassadors. I trust you can..." David looks at Skips and gasps. "Oh! Hey!" He points to Skips, then himself. "Bare chest, bare chest. Twins." David poses as one of his guards takes a photo of him and Skips. "That one's going in the album. Will you be with us for long?" He asked. "No, we unplugged a patch on this thing and we just need help re-synthesizing our friend." Mordecai said.

"Hm, shame. Well, seeing as you are the newest alien ambassadors we have, you may consider yourselves my honored guests. Let's head back to my office and see if we can get you sorted out." They all start traveling to David's office, checking out the city along the way. "As you can see, we have a society in which all our synthizens play music in perfect harmony." Everyone plays their synthesizers harmoniously, pleasing David. "Mm, not a note out of place." They pass by two synthizens,

Robert and Keith. Robert rides his synthesizer like a skateboard, creating a discordant tone. David gasps and plays an ominous tune on his synthesizer belt, summoning an event security robot. "Discord detected." The bot said. "Discord is cool!" The security bot captures him and Robert. "Discord is the lifeblood of modern music!" Keith shouted. "What was that all about?" (Y/n) asked. "He ended his song on an unresolved seventh. It's impossible to make that into a harmonious sound. I'm sorry you had to hear that." Mordecai and Rigby try to set Gary's synthesizer down, only for David to keep walking. "Let us continue to the palace." Rigby and Mordecai groan as they continue to carry the synthesizer.

"Skips, this is getting really heavy. Could you or (Y/n) just carry it for a little while?" Rigby asked. "Did we kill Gary?" Skips asked sternly. "No." The duo said reluctantly. "Then, there's your answer." Everyone arrives at the Synthos Palace, walking down a long hallway with holographic heads on display. "This is Harmon Hall. The portraits of all our previous heads of state ranging from: Moginious Vangeloworth to Lady Tronroeder, all the way up to...." David walks past the one that mysteriously says "Out of Order") "to myself, of course. What do you guys think?" (Y/n), Mordecai, Rigby and Skips compliment the hologram at once. "Can you just take us to your office, so we can re-synthesize our friend?" (Y/n) asked. David smiles. "A woman of business. Let's get to it."

(David's office)

"So, you need to reload your friend's patch?" David turns around as the office shows a giant synthesizer keyboard as a floor. "Well, you guys seem to have a bit of a problem, don't you?" He asked. "Yeah, and we're really sorry, but could we please set this down somewhere?" Mordecai asked, and David chuckles. "I know you're new here, but I'm afraid setting that on the floor would create a discordant tone." He said. "Ugh! Stupid really cool floor." Rigby said.

David pulls out a holographic web page. "Do you know anything about his patch combination? His base waveform?" He asked. Skips shows David a photo. "Well, here's a picture of him." He said. David sees the picture, which was taken from "Skips Strikes" "Hmm. Ah, yes. Yes, I do remember him. His name is Gareth, correct? We must get to the re-synthesizing studio at once." He leads them to a "studio" "And, right through here is the re-synthesizing studio." Everyone sees the two arrested synthizens from before.

"Hey, what are those guys doing here?" Mordecai asked." David plays the same tune from earlier, sealing the door, to (Y/n)'s, Mordecai and Rigby's confusion. "I'm sorry, but I simply can't let you re-synthesize Gary. He's the most wanted criminal in all of Synthos." David said. "What?" The four asked in shock. "His experimental jam sessions nearly destroyed this world. And your association with him makes YOU all criminals as well!" David shouted. "What's gonna happen to us?" Skips asked. "Oh, the same thing we do with all discordants. You'll be shot into our sun, The Synth Star." The hatch opens to show the sun. "Ciao, then." David said. "Hey! Hey, let us out!" (Y/n) demanded. The rocket reaches ground level, as the synthezens protest to this.

"Let's tune out for our execution." Robert said. "Yes, quite." Keith said. The rocket prepares to launch. "10 seconds to launch." Skips, (Y/n), Mordecai and Rigby try to break free. "Don't bother! There's no way you're punching through that futuristic material." Keith said. "I believe you talents call it "tempered glass". Robert said. "Glass? Guys! Your patch from the garage!" Skips said. "Ten, nine, eight, seven, six, five, four, three, two..." Mordecai and Rigby re-plug the cables the same way they did before. Rigby then plays some keys as  (Y/n), Mordecai and Skips cover their ears. "Mmm. Dig that crazy sound." The sound shatters the rocket's glass. Gary's hologram emerges from the synthesizer. "YOU GUYS!" Gary said angrily, with a distorted voice.

Synthizens gasp and recognize Gary's face as everyone lands back on the ground, with Skips holding onto Gary's synthesizer. "That's Gareth's synthesizer." Keith said. "Yeah, you guys know him?" Rigby asked. "He's the rightful King of Synthos." Keith said. "Wha-? He's not a criminal?" Skips asked. "No." Robert and Keith project a holographic screen from their eyes, featuring David, a security bot, and Gareth with his synthesizer. "After Gareth's disappearance 200 years ago, David seized the throne. Before long, he completely outlawed anything challenging. We've long awaited the return of Gareth and his forward thinking taste in music." Robert said. Mordecai gasps. "The patch! That's exactly what we need!" He said.

"Now you know the truth. I won't let you re-synthesize Gareth." David plays the ominous tune, activating the security bots next to him. "You guys work on Gary's patch." Skips said. "Guys, we need to copy the hologram." Robert and Keith nod, as they lower the hologram to their level. (Y/n), Mordecai and Rigby look at each other as they proceed to fix the patch. Skips jumps onto one of the bots and proceeds to destroy it. (Y/n) fixes one of the cables, Rigby hits a key. Gary's physical form appears distorted. "We almost got him." (Y/n) said. "Try the ring modulator." Robert said. "The what?" Mordecai asked. "The round one, with the knobby thing on it." Mordecai turns the dial Robert specified, nearly straightening Gary's body. Skips has destroyed the robots, prompting David to fire a stun laser at him.

"Jam session's over, boys." David said. "Skips!" (Y/n) notices a loose cable. "Rigby, the low-pass filter." Rigby adjusts that cable, restoring Gary's patch. David gasps. "No!" Gary reappears; the synthizens mutter in excitement. "It's him. It's really him." Keith said. "I'm so excited, I can barely contain myself." Robert said. "Hello, David. My half-brother." Everyone gasps. "Wait, what?!" (Y/n) asked. "Oh, hello Gareth. So good to see you again." David said. "Don't play coy with me. I heard everything, David. And, it's not cool." Gary said. "Dude, are you really the King of Synthos?" Mordecai asked. "I'm back. So, it appears as though I am.

Synthizens of Synthos, I formally challenge David's right to the throne." Gary said. "You'll rue this day, Gareth." David said. Nearby synthizens play their synthesizers as David projects a holographic keyboard from his belt and Gary summons his synthesizer to him. David begins to play a harmonious sound on his synthesizer, shocking (Y/n), Mordecai and Rigby. Gary starts to play his own tune in response. David turns his flat keyboard into a round one,

playing a more complex tune that levitates himself off the ground. Gary proceeds to do the same with a discordant tone. "Gary, Gary, Gary, Gary!" Everyone chanted. David gasps as Gary plays a harmony through discord. "Discord?! It's im-possible!" He shouted. "Nothing's impossible... through music!" Gary's final notes create a blast that hits David, sending him onto the rocket. "Launch resumed." The rocket is launched. "Thank... you." The rocket makes an impact with the Synth Star. The Synth Star destroys the rocket and David's body. David's synthesizer belt lands back on the planet floor. "Did you just kill your half-brother?" Rigby asked. "I merely destroyed his physical form." Gary said.

"Don't worry. We've got this." Robert and Keith pull out baseball bats and destroy David's belt. "Dude, that's dark." Mordecai said. "It is the way of Synthos." Skips said. "Why did you leave us, Gareth?" A Synthizen asked. "I hid my synthesizer in Skips' garage to encourage myself to travel the galaxy, before returning as your king. But, if there's one thing I've learned in my travels, it's that you can't rock with rules. I may be your king, but I am not your ruler. From this day forth, there shall be no ruler of Synthos. Let music guide you for the rest of your days." Gary said.

"True. (I agree.) [He'll always be king of my heart.] (Wow.)" multiple Synthizens said. "Whoa, that's pretty awesome." (Y/n) said. "Sorry we changed your patch, Gary." Mordecai said. "Yeah. Won't happen again, probably." Rigby said, and (Y/n) slaps him. "Ow!" He shouted. "We rock stars have no need for apologies. Now, let's blow this thing. Wings are on me." Gary snaps his fingers, summoning his car and the Guardians of Eternal Youth. "Finally! Now, can we please go to the mall?" Reginald asked.