It Came From Next Door is the first half of episode 1 of season 1. It first aired on Nickelodeon in the United States on August 1, 2003.
Jenny (also known as XJ-9, a crime-fighting teenage robot girl created by Dr. Wakeman to be Earth’s protector) makes her first contact with the outside world, meeting Brad and Tuck Carbunkle for the first time. While Brad immediately accepts Jenny as a new friend, Tuck does not quite see her as anything other than a "evil robot cyborg".
Tuck, while practicing baseball, hits a ball that flies through a window in neighbor Dr. Nora Wakeman's front door. His brother Brad instructs him to get the baseball back, but when Tuck knocks at the door, nobody arrives. He wanders inside, seeing various pieces of machinery and robot parts strewn about. When he reaches the baseball, it is handed to him by a shadowy, imposing figure, later revealed to be XJ-9. Tuck flees in terror without taking the ball, where he is intercepted by Brad and informs Tuck that he encountered a "hideous bloodthirsty robot". Ms. Wakeman overhears this conversation, and Brad tries to explain the situation, but Wakeman slams the door in his face, so he leaves, only to notice the robot while arguing with his brother.
Dr. Wakeman walks back into her house berates XJ-9, who prefers to be called "Jenny", for having left her room and instructs her that she must not encounter any of the human population, especially teenagers. She instructs Jenny that there is a meteor warning, but Jenny disregards it because most meteors typically burn up in the atmosphere. When Dr. Wakeman leaves the room, Brad climbs in through Jenny's window and meets her. The two leave and hang out, playing hackey sack and chasing ice cream trucks, among other things, while Tuck reluctantly tags along, still suspicious and nervous about Jenny. However, while they were playing, the hackey sack which Jenny booted through the atmosphere became part of the meteor, rendering it a “planet destroyer” class.
Jenny rockets off to destroy the meteor as soon as she gets the warning, and dispatches it quickly. As she returns to Earth, she and Brad realize in shock that Jenny had accidentally taken Tuck along with her, as he had been inadvertently attached to her wings. While Tuck is a bit charred from re-entry, he is impressed by Jenny's abilities and declares her to be "so cool!", now no longer afraid of her.
Dr. Wakeman oversees this, and decides that giving XJ-9 some time off couldn't hurt. However, the camera pans out to outer space, where several (presumably hostile) spaceships are closing in on Earth...
Tuck: R-R-ROBOT!!! There's a robot inside! A hideous, bloodthirsty robot!
Jenny: If this D-class dingus destroys the Earth, Mom'll dismantle me!
- Brad is the first character to appear in this episode. Tuck is the first character to speak in this episode, and in the series as well.
- One of the disassembled robots in Mrs. Wakeman's house looks suspiciously like Larry 3000 from Time Squad.
- There is a poster of a boy band in Jenny's room that resembles former boy band N*SYNC, titled SYNC'N.
- The title is a reference to an often used sci-fi title "It Came From...", which may have begun with the film It Came from Outer Space.
- This episode is a remake of the Oh Yeah! Cartoons short My Neighbor was a Teenage Robot.
- On the wall of monitors of various different cities, Beijing is listed as Peking. Peking is the pronunciation according to an earlier form of romanization of Chinese; the adaptation occurred in 1949. It is possible this is an intentional anachronism.
- At one point in the episode, Tuck refers to Jenny as a "robot cyborg." While this may have been for comedic effect, or possibly to underline Tuck's initial fear and suspicion of Jenny, cyborgs are not the same things as robots. The term "cyborg" is short for "cybernetic organism." In order for Jenny to be a cyborg, she would need to be at least partially organic.