The series begins with Ned finally scraping up enough money to buy a pet. However, upon reaching the pet store, the only thing he can actually afford is a newt. Dubbing his new pet “Newton”, Ned quickly tires of it, since Newton just lies on the rock in his bowl. Complaining to the pet store owner that his new pet is not very active, the owner gives Ned a can of “Zippo for Newt” pet food but warns Ned not to give his pet too much. Ned feeds Newton a little, but Newton does nothing. Ned leaves the can beside Newton’s bowl and goes to bed.
That night, Newton crawls from his bowl and gulps down several mouthfuls of Zippo. Thus, the “too much” warning comes true: Newton grows 6 feet tall, can talk (voiced by Harland Williams), and has the power to shapeshift. After Ned realizes this, he and Newton become the best of friends, but unfortunately, the effects of Zippo do not last forever. In fact, Newton often gets Ned into trouble, at which point the Zippo wears off and Newton shifts back to his smaller form, leaving Ned alone to bear the wrath of his elders.
The series recounts the misadventures of Ned attempting to live a normal life while trying to keep Newton from being discovered. Recurring plots involve Ned and Newton working to fix situations which Newton has helped go awry, Ned’s hopeless crush on his neighbor, Linda Bliss (who reduces Ned to speaking in gibberish) and his rivalry with snobbish Rusty McCabe for Linda’s affections.