Mr. Wilson is painting his house and Dennis invites himself over to help out. Needless to say, Dennis' "helping" gets Mr. Wilson close to a nervous breakdown. Dennis accompanies Henry to an auto showroom, where Dennis harasses the poor salesman so, that Henry buys a new car almost to avoid a law-suit. He discovers that the purchase entitles him to watch the actual car being built on the assembly line, with the hapless salesman acting as their guide. Now Dennis turns his impulsiveness toward the robot assembly line, screwing it up completely, and their "new" car comes out looking like futuristic junk!. A Raymond Chandler-type takeoff in which Dennis pretends to be a hard-boiled private eye, in the Bogart tradition, tracking down his missing pooch, Ruff, by questioning his friends and neighbors.

An alien from another planet lands in Dennis room in a quest for peace and quiet... but Dennis wants to show him around! A mad romp ensues with Dennis taking the alien to Mr. Wilson's house.

Mr. Wilson slips on Dennis' skateboard and has to go to the hospital. Once there, Dennis arrives to cheer Wilson up... Wilson is in for the time of his life! The kids discover an abandoned old gothic house that Dennis decides would make a great club-house.

They're shooting a "Jaws"-type movie at the beach, when the remote control falls into the mechanical shark's mouth, and it zooms off. Dennis finds the fake shark, and crawling inside it, has fun frightening his friends.

Dennis and his family visit Mt. Rushmore, which is in the middle of being renovated. Dennis scales the scaffolding in an effort to help out. There he meets an old man holed up in one of the president's nostrils.