Dennis attempts to inject his grinchy neighbor, Mr. Wilson, with the holiday spirit, but causes his usual array of damage along the way. Dennis also hopes with his good deeds, that he will receive a new bicycle for Christmas. However, because of all of his accidents, Mr. Wilson threatens Dennis' parents with lawsuits and forces them to pay for damages, as well as losing his temper to Dennis, by telling him there is no such thing as Santa Claus. The Angels of Christmas Past, Present, and Future intervene to help save Christmas for the Mitchell and Wilson families. The Angel takes Mr. Wilson to his childhood home in the 1950s, where he runs to his bathtub to put his neighbor's model boats which he thinks are in the wrong place, when the nozzle breaks and floods the room. Mr. Wilson was like Dennis himself when he was a child. The Angel then takes him back to the present, and Mr. Wilson sees Dennis's parents do not have enough money for presents as a result of having to hand over so much money to the Wilsons in order to fix the damage caused by Dennis's behavior. They will have to sell the house to pay off Mr. Wilson's damage and Dennis lost hope in Christmas since he won't get the bike and calls himself a menace since he let Mr. Wilson down. He also notices how depressed his wife is because she really wants to celebrate Christmas, but due to her husband's hatred for the holidays they are unable to; he soon realizes he must put an end to it. Finally, the Angel takes him to the future, where it is bleak and the atmosphere requires SPF 800 sunscreen because of global warming since 2019. His house is abandoned since Dennis and the Mitchells aren't here and after his wife died, he died alone, and Dennis is shown to be old, lonely, childless, friendless and having a dislike of Christmas. Dennis grew up to be Mr. Wilson and twice as bad hating Christmas as he is. Mr. Wilson realizes that what he had said was not true. It is the final epiphany that convinces Mr. Wilson to change his outlook on Christmas and makes him vow to celebrate Christmas with others. Mr. Wilson then wakes up to find himself back in the present, and spreads his Christmas joy around the neighborhood; Dennis wakes up the next morning with a tree loaded with gifts. Mr. Wilson helps Dennis's parents with finances, forget about the debt and knew a couple of people to repair his house and talks to Dennis and cheers him up with holiday joy the bike he always he wanted. Mr. Wilson and his wife have a big Christmas tree in their living room and his childhood fishing pole was purchased online. Dennis races with the other kids on his new bicycle, and loses. The film ends with the Angel sitting on a roof reflecting on how much he loves happy endings before popping back to the North Pole, and the kids riding their bikes before Dennis accidentally crashes into Mr. Wilson, ending the film.
