A couple of kids build a giant metal robot named Delbert. Junior's mother calls him in to take his nap and they accidentally leave the robot on. The robot breaks out of the garage and starts into the city. Junior sees the robot go by and chases it.
A man in a car beeps his horn at Delbert and Delbert picks up the car and smashes it. He then starts smashing other things as well. Junior runs to Atom Ant's anthill and asks for help in stopping the robot. Atom Ant tries to stop the robot from causing too much destruction and has to save a bus from being thrown to the ground and stop Delbert from pushing a building off a cliff.
Delbert then uses a round stone as a bowling ball and Atom Ant has to get everyone out of the way and smashes the ball. The robot then crashes a plane on a runway.
Atom Ant catches up with Delbert and smashes the robot into pieces. Atom Ant reconstructs the robot into a kiddie ride.