(Episode begins with Mordecai and Rigby lounging on the golf cart.)

Mordecai: Dude, what are we going to do this weekend? Nothing's going on.

Rigby: I don't know.

(Sound of the cart coming towards Mordecai and Rigby.)

Mordecai: (gasps) Dude, it's Benson.

(Mordecai and Rigby quickly gulp down the soda, throw the cans away, and clean the cart, as Muscle Man drops off Pops and Benson.)

Muscle Man: (reminding Benson) Alright, so that's tonight. Don't forget it.

Benson: We'll be there.

Muscle Man: See you there.

(Muscle Man drives away in the cart.)

Mordecai: What was that all about?

Rigby: I don't know.

Pops: Oh, Mordecai and Rigby. What costumes are you going to wear?
Mordecai and Rigby: Costumes?

Benson: Muscle Man's throwing a birthday party for Hi Five Ghost. Apparently, it's a costume birthday party.

Rigby: Let me see.

Mordecai: Ah, what? It's invite only.

Benson: You guys got invited, right?

Mordecai: We didn't even know there was a party. Did you know there was a party?

Rigby: No, I did not.

Mordecai: We didn't even know there was a party.

Benson: Oh, well... (snatching the invitation) Maybe you weren't invited.

(Mordecai and Rigby stared at each other. Scene cuts to Muscle Man putting a lot of cans of soda into an ice bucket.)

Mordecai: Hey, Muscle Man. Uh... we heard that you're having a party tonight. What time should we show up?

Muscle Man: (dumping three cans of soda angrily) NEVER, YOU'RE NOT INVITED!

(Muscle Man then dumps the last few cans of soda into the ice bucket and drives away. Scene cuts to the House.)
Rigby: Ugh! Dude! What's his problem? Why won't he invite us to his party?

Mordecai: Dude. I know why he's not inviting us to the party.

Rigby: Why?

Mordecai: Remember when you were choking this morning.

(Scene cuts to that day's morning, Rigby is choking loudly in the kitchen.)

Muscle Man: (chuckling) Look at Rigby's face.

Mordecai: Oh no, he's choking! (walks over to Rigby) Don't worry, dude. I gotcha.

(Muscle Man continues laughing until Rigby throws up his spit wad, which then gets in his soda and splashes in his face.)

Muscle Man: (disgusted) Aw, sick! Your choke wad spat soda in my face! (whining hysterically)

(Scene cuts back to the present.)

Rigby: Dude, that wasn't our fault, I was gonna die. And besides, we got him a new soda.

(Scene cuts back to the morning as Muscle Man is still whining about the soda on his face.)

Rigby: Ugh, quit whining. Here's another soda, you big baby. (holds the glass of soda, but trips over the soda can, splashing more soda into Muscle Man's face) Uh oh...
(Muscle Man then goes into a ballistic frenzy, pushing the table against the wall, then whamming on it, and lying on the floor still whining. Scene then cuts back to the present again.)

Mordecai: Yep, that's probably why he's not inviting us to his party. We gotta go apologize.

(Scene cuts to M&R walking to Muscle Man's trailer. Rigby then knocks the door.)

Muscle Man: What?

Mordecai: Hey, Muscle Man. We're sorry about that soda thing this morning, so we bought our console as a peace offering. You can borrow it for your party.

Muscle Man: One, I don't know what you're talking about and B, I'm busy. But I'll still take your video game. (swipes the system from Mordecai and Rigby, then closes the trailer door) Yo, H.F.G.! I found a video game system on the ground. Let's see what happens when we put it in the microwave.

Rigby: Dude, you said that was gonna work.

Mordecai: (sighs) I know, I know.

Rigby: He'd better not trash our system. That thing wasn't cheap.

Mordecai: Come on!

(Scene cuts to later when M&R drive the cart and see Muscle Man prepare the decorations for the party.)

Rigby: Ugh! Man, he's not gonna invite us. We already said sorry. What else can we do?

Mordecai: (comes up with an idea) Oh, I know what to do.

Rigby: What?

Mordecai: We just have to make Muscle Man think that we don't wanna go to his party.

Rigby: What?

Mordecai: Reverse psychology. If he thinks we're not into it, then he'll really want us to be there.

Rigby: Ohhhhh...nice.

Mordecai: Just act like the party's lame and watch the invitations come rolling in.

Mordecai and Rigby: Hmm hmm hmm hmm hmm hmm hmm hmm! (Driving the cart over to Muscle Man as he is in the middle of the decoration preparation.)

Mordecai: Muscle Man, we don't wanna go to your party.

Muscle Man: Good, because I wasn't gonna invite you anyway, so get lost!

Mordecai: Muscle Man, we're sorry about the soda.

Muscle Man: What are you talking about?! I said GET LOST!!!

Mordecai: Ugh, forget it. (hits the gas pedal, spins the cart, and drives away.)

(Scene cuts to the House at nighttime. Mordecai and Rigby are lying on their beds.)

Rigby: (sighs) Wanna play some video games?

Mordecai: We gave away our system, remember?

Rigby: Well, whatever. The party's gonna be lame, anyway. It's just gonna Pops, Skips, and Benson sitting around doin' nothing.

(Mordecai and Rigby sit up as they hear thumping bass music from outside. Looking out the window they see what appears to be a rocking party taking place in a tent in the middle of the park.)

Mordecai and Rigby: Whoaaaa...

Mordecai: Dude, forget the invitation. Let's just crash it.

Rigby: Yeah.

(The scene cuts to outside the party. A bunch of unidentified guests are in costumes. Mordecai and Rigby show up wearing unconvincing cat and dog masks, respectively/)

Mordecai: Dude, this is amazing.

(They encounter a huge, muscle-bound bouncer, Bobby, at the tent entrance/)

Bobby: Hold up! You're not on the list.

Rigby: What? How do you know we're not on the list?

Bobby: Name?

Mordecai: Mordecai and Rigby.

Bobby: (checks list) Not on the list! I can only let people in that's on the list. (to another guest who walks past) Yo, hold up! You're not on the list.

(Muscle Man appears at the window.)

Muscle Man: Ey, yo, Bobby! You can let that guy in. He seems legit. Wooooo! Let's keep this party goin'!

Bobby: (to Bobby, showing him inside) Right this way, sir.

Mordecai: Aw, what? He didn't even have a costume.

Rigby: Yeah, what the H, Bobby?

Mordecai: Dude, let's go. (Mordecai walks away/)

Rigby: Wait, where you goin'?

Mordecai: We're gonna get into this lame party.

(Mordecai and Rigby appear around the back of the tent house, without their masks on.)

Mordecai: Dude, come on. We'll just go through the window. (Mordecai struggles to open the window. A ghost, looking exactly like Fives except with stubble, appears through the tent wall holding a soda can and wearing shades.)

Lo-Five Ghost: Hoo! Par-tay!

Rigby: Hey, it's fives!

Mordecai and Rigby: Happy birthday, fives!

Lo-Five Ghost: What?

Mordecai: Whoa, sorry. We thought you were someone else.

Lo-Five Ghost: (laughs) Dude, I'm not Hi Five Ghost, I'm his brother, Lo-Five Ghost. What're you guys doing out here? The party's inside! Woo!

Mordecai: Haha, yeah... we... weren't really invited.

Lo-Five Ghost: What? Why not?

Rigby: That's what we wanna know. We don't really care - we just wanna get in.

Lo-Five Ghost: OK, look. I'm not supposed to say this but, if you really wanna get into the party, I can turn you into a ghost.

Mordecai and Rigby: Really?

Lo-Five Ghost: Yeah, then you won't have to go through the door. You can go through the wall. Plus, your costumes will be a lot more believable. So, what do you say? You guys wanna do it?

Mordecai: Let's do it!

Rigby: OK, yeah!

Lo-Five Ghost: Ha ha! Alright! Up high, Down low...

(The two are transformed into ghosts by the power of hi- and lo-fiving.)

Lo-Five Ghost: ...Now you're ghosts.

Mordecai: Aw, man. This is so cool...

Rigby: Dude, dude, punch me in the face!

Mordecai: OK.

(Mordecai swings a punch at Rigby, who squeals in pain.)

Rigby: Nooooouuaaaoow! I thought stuff's supposed to go through us.

Lo-Five Ghost: Well, yeah, real stuff if you want, but not other ghosts. Woooooo! Party!

(We cut to inside. Pops is dressed like an ice cream cone, Benson like a vampire, and Hi Five Ghost is wearing an eyepatch.)

PPP: Mordecai and Rigby, hello!

Mordecai: Hey, happy birthday!

Rigby: Yeah, happy birthday!

Hi Five Ghost: Thanks!

Benson: So, you guys got invited after all?

Rigby: Hmm! Hmm!

Mordecai: Hmm! Hmm! You could say that.

Pops: What wonderful costumes!

Rigby: Ha! These aren't costumes.

Hi Five Ghost: Wait, those aren't costumes?

Mordecai: Yeah, no, we're totally ghosts.

Rigby: Yeah, your brother turned us into ghosts so we could sneak in here and wish you a happy birthday.

Hi Five Ghost: Oh no. This is bad.

Rigby: Yeah, we're bad. We do whatever it takes to party! (Rigby hi-fives Mordecai.)

Mordecai and Rigby: Ha ha!

Hi Five Ghost: No, you've got bigger problems. If you don't get turned back into yourselves soon, you'll be stuck as ghosts forever.

Mordecai and Rigby: What?

Mordecai: Well change us back!

Hi Five Ghost: I can't. I don't know how.

(Cuts to across the room, where Hi Five Ghost angrily confronts his brother at a snack table.)

Hi Five Ghost: Dude! You turned them into ghosts?! Change them back!

Lo-Five Ghost: I don't know how to! But... maybe dad knows.

(Back in the middle of the party, they speak to Hi Five Ghost's Father.)

Hi Five Ghost's Father: Hmm. Not good. Not good at all. If you want to turn back into yourselves, you have to scare someone.

Mordecai: Scare someone?

Hi Five Ghost's Father: Yes. It's the only way.

Mordecai: Dude, let's scare Muscle Man. He doesn't know we're here yet, so he won't be expecting it.

Rigby: OK, let's do it!

(Muscle Man appears at the top of the stairs.)

Muscle Man: Oh, man! I gotta use it!

Mordecai: He's going to the bathroom. Quick, hide!

(They run into the bathroom and turn off the light. Muscle Man opens the door and turns on the light, at which point Mordecai and Rigby scream at him. Muscle Man yells in shock, and grabs his chest, falling to the ground.)

Rigby: What's he doing?

Mordecai: Oh no. He's having a heart attack!

(Mordecai and Rigby drag Muscle Man into the party room.)

Mordecai: We need a doctor!

Hi Five Ghost's Father: Everyone back up, back up! What happened?

Mordecai: We scared him... and he fell over!

Hi Five Ghost's Father: OK, step back, let him breath. (He checks his breath) He's not breathing! (He begins administering CPR) ... he's gone.

(The crowd gasps in horror as Hi Five Ghost's Father closes Muscle Man's eyes for the last time.)

Hi Five Ghost: Oooooooooaaaaugh! You killed my best friend!

Mordecai: We're sorry!

Rigby: Yeah, we didn't mean it!

Mordecai: We just wanted to get into the party.

(On the ground, Muscle Man's eyes open a tiny bit, before he speaks/)

Muscle Man: Got you, dudes. Ha ha ha ha! Best, Prank, Ever! (Muscle Man laughs and whoops.)

Mordecai: What?! What's wrong with you?!

Rigby: This was a prank?!

Muscle Man: (laughs) Yeah, it was! And you two fell for it!

Benson: Wait. I thought you invited us to a costume party.

Muscle Man: I did. But that was just the beginning of my plan.

(A flashback montage begins, narrated by Muscle Man, showing everything he describes.)

Muscle Man: When you jerks spilled soda in my face, I knew I had to get you back. That's when I decided to throw a party. I invited people and I made sure that you were aware of that. Then we bailed Fives' brother out of jail so he could turn you into ghosts.

(The montage ends.)

Muscle Man: It was the ultimate prank. The ultimate payback.

Mordecai: Wait... but if you wanted to prank us at the party, how come you didn't invite us?

Muscle Man: Easy: not inviting you was the only way I knew you'd show. It's called reverse psy-cho-logy, babies! (Muscle Man pronounces the ch- in psychology like the ch- in chew) Ha ha ha ha!

Mordecai and Rigby: Augh!

Rigby: This is the lamest and most expensive prank ever.

Muscle Man: Ha ha ha ha! And it was worth it. Maybe next time you'll think twice before spilling soda in my face.

Mordecai: Yeah, we'll definitely think twice.

Benson: Alright, I'm out of here.

(The guests all start to leave.)

Muscle Man: Ha ha ha ha! Where you guys goin'? Thee's still plenty of food! (Muscle Man begins to stuff his face with food and laughs) Ha ha ha ha!

(Muscle Man begins to choke.)

Rigby: Oh, dude, Muscle Man's choking! (To Hi Five Ghost's Father) You have to help him! You're a doctor!

Hi Five Ghost's Father: No, I'm not a doctor. That was just part of the prank. Does anyone know the Heimlich?

(The remaining guests look to each other helplessly.)

Rigby: Mordecai knows it.

Mordecai: Yeah, right, he's just faking it. As soon as I help him, he's going to be all (mimics Muscle Man's voice) Got you again, dudes. (Switches back to his normal voice) I'm sick of it.

Rigby: Ah, lame. Dude, are you pranking us?

(Muscle Man shakes his head as he continues to choke. He falls to his knees.)

Mordecai and Rigby: Dude, he's not pranking us!

Mordecai: I got you Muscle Man, I got ya!

(Mordecai performs the Heimlich and gets the food out of Muscle Man's throat.)

Mordecai: I hope this makes us even.

Muscle Man: It does. Lo-Fives, change 'em back.

(Lo-Five Ghost clicks his fingers and returns Mordecai and Rigby to their normal selves.)

Muscle Man: I'm sorry I pranked you guys so hard. Look. It's gonna be a real party, and you guys can stay if you want to.

(Muscle Man offers his hand, and Mordecai shakes it.)

Benson: So, seriously. Is this a real party or not?

Muscle Man: Does this answer your question?

(Muscle Man waves a cassette tape, then throws it towards the tape deck, but misses.)

Muscle Man: Aw.

Benson: No. Doesn't really answer my question.

Muscle Man: I thought I could get it in the tape deck. (Walks over to and picks up the tape). Here. Does this answer your question? Everybody, party! (The music starts and the guests all dance.)

Mordecai: Can you believe this?

Rigby: No. Hey, next time you see Muscle Man with a soda, can you remind me not to spill it in his face?

Mordecai: Yes. Yes I can.

(Muscle Man appears with an odd-looking video game system.)

Muscle Man: Hey guys. I thought you'd like to have this back.

Mordecai and Rigby: Aw, thanks.

Mordecai: Hey, wait. Is this just paper mache?

Muscle Man: Yeah, sorry guys. I sold the real one to a pawn shop. It was all a part of the prank.

Mordecai: Are you serious?

Rigby: What's wrong with you?

(Muscle Man pulls the real console from behind his back.)

Muscle Man: Got ya, dudes. (The episode ends)