This episode starts out with Zim pressing buttons on his ship. This takes a while because the credits are going on too. It finally shows a whole bunch of ships flying, and this man saying welcome to Conventia, the convention hall planet. He also tells them to take the complementary teleporters to the planets surface. There are a billion aliens walking into the convention hall to get there seats. The man talking presents the leaders of the race of aliens, known as the almighty tallests. The tallests come down waving, and red says that he knew that the people would love the laser show. Purple tells him that smoke machines are what really works, and he gets hit in the eye with a laser.
The tallest welcome all the soldiers, telling them that they are all great soldiers, but the ones that are standing behind him are the ones that are the best, and chosen for "Operation: Impending Doom II." He tells them that they are all assigned to a planet, and that they will blend in with the inhabatants of the planet, and gaining all knowlage of the them, making them easier to conquer.
The first invader is assigned to the planet Vort, home of the universes most comfortable couch. They call out invader Spleen, but they don't show what planet he gets. It cuts to a guy coming in late, screaming for people to move out of his way. The next guy to come up is Invader Scooge. Because of his shortness, he is assigned to the planet Blorch: Home of the Slaughtering Rat People. They say that that concludes "The Great Assinging" and that they can help themselves to some nachos. The guy that was screaming for everyone to move out of the way is revealed as Invader Zim (the tallest hate him).
Zim says that he's sorry he's late, and that he couldn't find his invitation, and that they were lucky he made it. The tallest tell him that he was invited at all. Purple asks if he was banished to Food Courtia, and if he should be frying something, and Zim says that he quit when he found out about the assigning. They tell him that the assinging is over, and Zim claims that they can't have an invasion without him, and that he was in Operation: Impeding Doom I. They say that they remember and they go to a flashback.
The flashback shows alarms going off and building being blown up and stomped on by a huge robot. Inside the robot is Zim. A guy says to him that they are on their home planet, and Zim tells them to twist some more knobs and pull some more levers.
Zim claims that he put the fires out, and the tallest say that he made them worse. Zim comes back with "Worse? or better?" They tell Zim that no invader has been so small, and that he was very small, a tiny thing. He claims that the invader blood runs through his veins, like giant radioactive rubber pants, the pants command him, and not to ignore his veins. Red says that as a show of gratitude for his service in the past, that he is awarded a sandwhich. He says that an oppertunity to prove himself as an invader is all that he asks, and to give him. Red says that he has a plan, and tells Zim that he is truely deserving, and that they will send him to a planet so mysterious, that no one has even heard of it, and Purple adds that those who have heard of it, dare not speak it's name. Zim asks what the name is, Purple says he dares not speak it. He points to a note on the side of the map, that says planet with a ?. He tells all the invaders to go to the equipment hall.
The scene shifts to a boy on top of the roof, listening to the to headphones with a big satellite. He heard everything that the tallest said, and he said that they were coming. A little girl opens the refrigerator, and says that Dib drank the last soda, and that he will pay. Dib jumps off the roof, and into his house, and tells his dad that they were coming, that he was on top of the roof he heard the transmission of the aliens. He stops him, and tells him that he is making toast. He runs to his sister Gaz, and says that they are coming. She asks who, and he says that he don't know.
The scene goes back to the Irken empire, and the tallest are handing out Servie Issue Information Retreval Unit (SIR). He says that it will assist them on retreaving valuable knowlage of the planet. Red says it's also a thermos. Purple picks it up and screams, who wants this one, and someone screams that they do, and he throws it at them. Red tells everyone else to line up and take a robot.
The first guy tells his to warm up his ship engines, and he says that he obeys. Zim comes up and says that he finally gets a robot slave of his own. He holds his hand out like a little kid getting candy. Red says that they have a top secret model for him. He takes a trash bin full of disassembled SIR units and puts a new one together. Purple takes some of his pocket crud and puts it in the unit as a brain. He makes a noise like a line is coming down to bring him one and he throws it on the ground. Zim tells him that it looks kind of not good. Purple tells him thats what the enemy will think. Zim said it was very good and that it even fooled him. Zim said that he is honored to be trusted with such advanced technology. The SIR unit comes on and runs to Zim, saying, "GIR, reporting for duty." Zim asked what the G stood for and he said that he didn't know, and he starts going crazy. Zim asked if it was supposed to be stupid, and Pruple said that it wasn't stupid, it was advanced.
Zim is now in his spaceship with his disfuntional SIR unit, GIR. Zim tells GIR that there mission has begun, and that they are going to reign doom upon the filthy heads of their doomed enemys. Gir starts to sing the doom song.