Two and a half years after the events of the first film, Dennis Mitchell, [Justin Cooper], is worse than ever. He goes to the Wilsons’ house with a wild menagerie of pets as gifts for the birthday of [George Wilson], [Don Rickles], and his antics set off a chaotic but comic chain of events. The menagerie includes frogs, lizards, snakes, insects, tarantulas, scorpions, mice, exotic mammals, and even a baby alligator. The ordeal culminates with George accidentally riding down a flight of stairs in Dennis’ red wagon and his birthday cake splattering across his face, courtesy of his wife, Martha, [Betty White].
Soon after, Mr. Johnson, Dennis’s grandfather and Alice’s father-in-law (George Kennedy), shows up and unveils that he’s moving in, a development that has Dennis spending more time with him than with George. George, feeling the weight of aging, is ripe for temptation when two crooked con men—the Professor and his assistant, Sylvester, [Brian Doyle-Murray] and [Carrot Top]—try to lure him with a supposed “rare” root used to make people younger. By the time Dennis discovers that he already owns a similar item found somewhere nearby, George’s hopes begin to shift.
The con men return and manage to sell George a machine that allegedly makes people younger. Suddenly, the dynamics invert: Mr. Johnson starts to envy the younger mindset George exhibits, while George becomes more buoyant and confident. In the midst of it, Dennis is cleaning up a mess he accidentally made on Mr. Johnson’s car—tripping over his own dogged luck—and he inadvertently destroys George’s machine with a cotton-candy-like substance he mistook for soap. Consequences follow: Dennis is grounded after a spanking, and George announces that he and Martha will move away to escape Dennis’s chaos, though no one seems eager to follow through on that plan.
Seeing an opportunity, the Professor and Sylvester press George to rely on his new plan to squeeze more money from him. Dennis, almost by accident, helps the local police thwart them as they pose as various workmen at the Wilsons’ home, trying to drain George’s bank by stockpiling uncashed checks and insisting the house needs repairs before it can be sold. The uncashed checks are returned to George, who now hesitates to move after Dennis begs him not to.
Mr. Johnson, however, is determined to reclaim his camper, hoping to take Dennis to the Grand Canyon despite everything that transpired. The final act unfolds with Dennis and Mr. Johnson aboard the camper in the Grand Canyon; Dennis, craving a keepsake rock for George, ends up taking the wrong rock—the one under the camper—which rolls down the incline with Mr. Johnson still inside.
As Christmas settles in, George and Martha catch news of the strange events and Dennis explains them to the camera, while Mr. Johnson is airlifted to safety. Dennis then delivers a cheeky shoutout to George: “He’s a menace!”
> "He’s a menace!"
