Invader Zim and the Rumor Weed is the fourth film in the Invader Zim film series. It follows around Earth's greatest hero Invader Zim encountering something badder than the Lost World: The RUMOR WEED!
The episode begins immediately with the story, two boys named Ricardo and Danny are leaving a movie theater. They are met by the Milk-Money Bandit who demands $3.18, which was the exact amount of their milk money, but after he robs them he runs into Invader Zim on a neighboring rooftop, who brings him quickly to justice.
Following this, Zim stands on a rooftop reviewing his technique with GIR and Flynn, when he accidentally knocks a plant off the ledge. It falls into the sewer getting caught on some electrical telephone wires on the way down. The electrical charge and a gossiping woman on the phone, brings the plant to life, and the Rumor Weed is born. The next morning GIR is speaking before Ricardo and Danny's class at Kenslyburg Valley Elementary. He makes the comment that he must go home and "recharge his batteries". The children don't understand the expression (the phrase is just a figure of speech and in American English means to rest and relax), and come to the false conclusion that GIR must be a robot monster. As they are walking home, they run into a small Rumor Weed who extracts their secret and promptly passes it along. She quickly moves from yard to yard spreading the rumor. Lockso, Mr. Johnson, and IQ unintentionally contribute to the rumor, but Invader Zim proves impervious to it.
He gets a call from Mayor Jackson who informs him that weeds are taking over the city. He springs into action, trying to destroy the weeds by conventional means, but weed-whackers and shears have no effect. He returns to the Invader-Lair where GIR and Flynn have been doing research on the Weed. They study a map of Kensleyburg and discover that all the weeds are connected by a vast root system to a huge Mother Weed deep underground. Realizing that these Weeds are strong enough to break up sidewalks and smash through brick walls, they decide they must attack it underground, at its root.
Fortunately, GIR and Flynn have made some modifications to the Invader Zim-Mobile that enables it to bore holes in the ground. Zim is oblivious as GIR guides him into the underground sewer, and once inside the sewer they lose contact with each other. The Mother Rumor Weed finds him by his crashed vehicle, and Invader Zim, aware of how to stop her, fires his water gun and wins.
Meanwhile, GIR and Flynn have gone into Kensleyburg to try to get help. There GIR is astonished to find that the usually kind citizens are afraid of him and saying strange things about him. They ignore his desperate assertions that he is not a robot monster; the rumor has grown out of control. When the giant Rumor Weed crashes up out of the sewer and grabs GIR and Flynn, they refuse to save GIR's life, believing he is getting what he deserves, but plan to save only Flynn's life.
Danny's mother arrives on the scene and recognizes the absurdity of the rumor. She figures out that her son and Ricardo accidentally started the rumor and explains to them that "even if it's true God doesn't want us to tell stories that can hurt, he want us to spread nice words". Given a second chance, they decide to spread good words and are able to convince the citizens of Kensleyburg that GIR is not a monster at all, but a very nice man. As the word spreads, the Rumor Weed turns into a flower and GIR and Flynn are saved. Invader Zim then emerges from the sewer having changed his clothes to a black workout shirt and blue jeans and is quickly hushed by everyone else before accidentally starting the rumor again by saying, "Oh hey GIR...somebody told me you were a...monster?"
The episode is wrapped up in the Invader-Lair with GIR, Flynn and Invader Zim. They reiterate that God says that rumors are wrong and God wants us to say nice words about people rather than telling stories that can hurt. The verse is on the Invader-Computer "Reckless words pierce like a tongue, but the sword of the wise brings healing" (Proverbs 12:18).