Some years after the previous film, Dennis Mitchell is worse than ever. At the beginning of the film, he goes over to the house of George Wilson to offer him some pets as gifts for his birthday. These include frogs, lizards, snakes, insects, tarantulas, scorpions, mice, exotic mammals and even a baby alligator. This ordeal ends with George unintentionally riding down a flight of stairs in Dennis's red wagon and accidentally getting his birthday cake thrown in his face by Martha. Soon after this incident, Mr. Johnson, who is Dennis's grandfather as well as Alice's father and Henry's father-in law, shows up and announces that he is moving in with the Mitchells. Dennis starts spending more time with him than his annoyed neighbor. George, upset that he's getting older, gets tricked by two crooked con men, the Professor and his assistant Sylvester, who try to talk him into buying a "rare" root used to make tea to make people younger. George is about to pay $10,000 when Dennis comes by. Dennis then reveals that he owns a root of the same kind, which he says he found on a place where those abound. Soon afterwards, the Professor and Sylvester return and sell George a machine that allegedly makes people younger. Suddenly, the attitudes of him and Mr. Johnson reverse as the latter feels George's pain of living in the same neighborhood as Dennis, while he starts to feel youthful and happy. While Dennis is trying to clean up a pile of garbage that he accidentally threw on Grandpa's car while he was taking out the trash, he accidentally destroys Mr. Wilson's machine with cotton candy mix that he mistook for soap. As a result of this, George declares that he and Martha will be moving away to be away from Dennis for good, whereupon Mr. Johnson decides to move into their house, although no one seems to really want to carry out this plan. Overhearing everything, the Professor and Sylvester decide to use George's plan as an opportunity to get more money from him. Dennis helps the police catching the con men, who were pretending to be several different workmen at the Wilson house when they were planning to move, attempting yet again to drain his bank account by stockpiling a hoard of his as yet un-endorsed checks by claiming that the house needed several repairs before it could be sold. Dennis, who was a "menace" throughout the whole film, ends up being a hero. The police return the uncashed checks and Mr. Wilson decides not to move after Dennis begs Mr. Wilson to not move. Mr. Johnson, however, announces intentions to get his motor home back, having promised to take Dennis to the Grand Canyon, also because of everything Dennis has put him through. The film ends as Dennis and his grandfather are in his camper in the Grand Canyon and Dennis, wanting to take a rock home to Mr. Wilson as a present, accidentally takes the one from under the camper, causing it to roll down the incline it is parked on top of with Mr. Johnson still in it. While enjoying the Christmas season, George and Martha see on the news what has happened as Dennis explains to the camera and Mr. Johnson is being airlifted to safety. Dennis gives a shoutout to Mr. Wilson, which leaves him flabbergasted that he mutters to the viewers "He's a menace!".
Cast
Justin Cooper as Dennis Mitchell, a young boy who is a total disaster.
Don Rickles as George Wilson, the Mitchell's next door neighbor and Martha's husband who strongly dislikes Dennis
