The episode begins with a view of a video camera in front of Ra at Casper's manor. He then asks why they were doing this again. Casper (who was holding the camera) reminds Ra that their doing this for a survival report. Mantha bursts in the conversation and informs the boys that their in Deedstown "Where everything looks normal". A knock on the door is heard and Casper goes check it out. Three tiny creatures in space suits point lasers and a vacube cleaner at Casper, but he doesn't notice them and closes the door.
Casper tells Ra and Mantha that its probably just some kids doing a ditch and run on an abandoned manor. A knock is heard again and all three answer it. Ra asks who ordered some munchkin astronauts. He gets corrected by Mantha who claims that they are "outer worldy visitors". The kids rush back inside and present the aliens a basket of rotten fruit as gratitude for their arrival. However the aliens vaporized the basket and point their weapons at the gang. Casper suggests that those aliens could be hostile towards creatures. Ra then assures Casper that he has a defence against hostile aliens. Ra charges at the aliens and literally kicks them out of the manor. The gang decides that they should go see Jimmy for some info on hostile aliens.
The three explain their story to Jimmy at his bedroom. Jimmy asks why hostile aliens want to attack them, to which they have no idea. The blond boy tells Casper, Ra, and Mantha that they should probably go back to Scare School as the aliens won't find them there. Unknowingly to them, they are being watched by the aliens from out the window. They follow the creatures back to the ship and stow away as it flies off.
Back at Scare School, the gang go with their schedules as they still have to finish their survival guide. Outside, the aliens decide to split up and find their targets. Mantha is listening to her scream player while writing her part of the project at her dorm and closes the door for no good reason (hitting one of the aliens in front of it in the process). Ra is seen examining books at the library researching on how to survive. While the alien is climbing on a bookcase, Ra slides a book back in the case and accidently made the alien fall of the bookcase. Casper is seen in the history room doing his part of the project, but has a hard time trying to find out how many V's are there in "poison ivy". Ra and Mantha show up and tell Casper that someone is banging on the door. They guess that its probably Thatch in an attempt to sabatoge their project. They open the door to see that its a present. When they aproach it, the aliens come out and surprise the gang. The aliens fire their lasers at the kids, but they run back in the history room and use their desks as shields. They come out of their hide and see the aliens trying to seal them in.
While the aliens are sealing the door, Casper realizes that he and his friends are dealing with alien lifeforms that are here to obliterate every last creature three-by-three. Mantha finds some rope and silently picks it up. The zombie shows her lasso trick to the boys by aiming it on the aliens. She puts the tied up aliens under her desk and tells Casper and Ra that they should go to the science room just incase the aliens break free. They do so while the aliens are struggling to get free. At the science room, the gang find Jackies nuclear reactor and decide to make it more "inviting". Once the invaders arrive, they find a dance club in the science room. Ra disguides as a club host announces that the dance contest is free for tiny space dwellers, which made the aliens enter the nuclear reactor. Casper closes the reactor as it activates, seemingly burning the aliens. The kids open the nuclear reactor to see if the aliens are done, but their luck ran out as the aliens jumped to their faces (with one of them useing its vacube on Casper's head). The gang ran around the classroom untill they pull them off of them and lock them in the cabinet.
However, the aliens are shaking the cabinet untill it tips over. But the aliens are using their lasers to escape through the bottom part of the cabinet. Casper & friends are left with no choice but to use their most unusual measure. Once the aliens escape, the kids grab them and placed them in a pakage. Casper suggests Mt. Everest as its easier to spell, which they do so by mailing it through Cappy's ship. The gang enter through the main entrance only to find the aliens blasting them (good thing they missed). Ra admits that those little guys are getting on his nerves, so he ties the aliens into a rocket and has Mantha light it. The rocket blasts off all the way into the sky and the gang thinks that their gone. Their luck ran out again as the aliens come back with a moon rover. Casper then thinks that if they take a long walk, the aliens will be gone.
The gang immediately grab the aliens, put them in Thatch's locker, and blocked it with Frankengymteacher. Casper, Ra, and Mantha leave the school, take the viking ship, flew to the "fleshie" world, arrived in Egypt, and landed near an oasis. They think they lost the aliens, but the invaders come out of the water and point their weapons at the gang. Ra then throws them to an alligators mouth and suggests that they should walk to somewhere else. They went back into the viking ship, flew to Transylvania, went into an abandoned castle, and hid in an empty coffin. But, the aliens are already inside and blew up the coffin with the kids in it. Mantha realizes that it has become painfully clear that their up against indestructable beings that will stop at nothing untill she and the boys come to a torturous end. The gang then threw the invaders into a spiked coffin, take the viking ship, flew back to Scare School, and rush to the boys dorm.
A knock on the door is heard, but the gang are so worried that the aliens could be waiting for them on the other side due to the "Running Gag Theory". So they slowly open the door only to find nobody outside. The invaders (who have somehow got into the dorm) fire the lasers from behind and knocked Ra and Mantha to the hallway window, luckilly it didn't break. Casper rushes to the two and tells them that theories proven wrong can be so cruel. They quickly get up, grabbed the invaders, placed them in the bathroom sink full of water, and sent them down the drain. The kids then use dangerous chemicles and send them down the drain incase those tiny aliens climb back up. The gang believe that the invasion has been thwarted and decide to get back on their survival guide.
The next day at history class, Casper & friends are about to turn in their project untill Ra drops his pencil. Someone picks it up for him, but it turns out to be the invaders again. They fire their weapons at them, but they miss and vaporized their survival guide. Ra tells Casper and Mantha that the whole alien thing has gone to far. Mantha then mentions that those aliens have forced them to a stoop of retaliation that even Casper will never dare approach. Again, they grab the aliens, tie them up in a series of explosives, light the fuse, and try to leave the room. But before they could do that, it is already to late that the fuse has already run out. The entire school blows up leaving nothing but mountain of rubble and a flooded history class room. The gang (who are slightly burned from the explosion) see that the explosion didn't defeat the aliens. Casper then admits that the aliens have beaten them. Mantha finds it emberassing that they've been bested by a bunch of carnival prizes. Ra then wonders if this is the end of their after lives. The aliens fire their weapons at Ra and Mantha while Casper gets sucked into their vacube cleaner. All that is left is a pile of ashes with one having Ra's hat while the other with Mantha's hair.
Jackie's voice is heard and says excellent work. One of the aliens says thanks, takes of its helmet and is revealed to be Casper. The whole thing turns out to be a virtual reality video-game. Casper admits that its the ultimate video game. Ra and Mantha seemed to enjoy it even though they have been going through painfull measures. Jackie Hyde explains that he designed the game for rookie space cadets to safely train while battling potentionally hostile creatures. Ra asks what could be more potentionally hostile than him, Casper, and Mantha combined. Mantha mentions that they creamed the enemy, and it was themselves. Casper hopes that nobody will be emotionally scarred by witnessing what appeared to be their gruesome end. Casper, Ra, Mantha, and Jackie leave the dorm as they should go play some slug-by. The End