Dennis Mitchell (Mason Gamble) is a five-year-old boy who lives with his parents in Wichita, Kansas. Henry (Robert Stanton) and Alice (Lea Thompson), and is the bane of next door neighbor, George Wilson (Walter Matthau). One morning, Mr. Wilson pretends to be asleep in order to avoid dealing with Dennis. Dennis enters his bedroom, only to find him asleep surrounded by his prescription medication, and assumes he's sick. To make him feel better, Dennis flings an aspirin into his mouth with a slingshot which causes him to gag and spit out the aspirin, as Dennis flees home to his parents.When Dennis arrives home, his parents learn of the incident he had caused to Mr Wilson and are both angered, but because they are both working, Alice has to take him to stay at Margaret's house for the day. Dennis isn't too happy about this, because she is mean to him. When he arrives, he and Margaret, along with his best friend Joey, venture into the woods to an abandoned tree house and intend to fix it up. Later, while getting paint from a high shelf in the garage, Dennis tries to grab his slingshot, which was taken away from him by his father Henry, and accidentally spills the paint on the ground. He then fervently attempts to vacuum it up, but ends up spilling a glob of paint as it splinters into Mr. Wilson's barbecue grill, while he's cooking chicken, and Mr. Wilson tastes the paint and wood splinters as he eats it. That night, Dennis has a set of babysitters; Polly and her boyfriend, Mickey. He plays doorbell pranks on them and they retaliate by sticking a thumbtack on the doorbell and preparing water and flour to dump on the prankster. However, Mr. Wilson goes over to Dennis's house to prove that Dennis was responsible for the paint in his chicken, against the wishes of his wife, Martha (Joan Plowright), only to ring the doorbell, prick his thumb, and get water and flour dumped on him, much to Martha's amusement. The next morning, Dennis goes over to the Wilson's house to apologize for the events of the previous evening, but finds himself playing with Mr. Wilson's dentures, losing two teeth down the drain, and replacing them with Chiclets gum in the process. This gets noticed when Mr. Wilson gets his picture taken for the newspaper. Meanwhile, a burglar named Switchblade Sam (Christopher Lloyd) arrives in town and begins robbing people's houses, as well as stealing things outdoors and striking fear into children he meets.Unfortunately for Henry and Alice, they have a difficult time getting people to watch Dennis while they both work. Unfortunately for Mr. Wilson, he and Martha are being charged with the task of caring for the troublesome boy, as both of his parents are being called away on business trips on the same weekend. Martha loves him as if he were her own grandson, as she and George have no children, and she enjoys telling Dennis a bedtime poem that her mother told her. Alternatively, George is further irritated by the boy who spilled bath water on the bathroom floor, replaced his nasal spray with mouthwash, and his mouthwash with toilet cleanser, even brought his pet dog Ruff into the house for a while.Fortunately for Mr. Wilson he's been selected to host the Summer Floraganza, a long awaited summer event. He has been growing and nurturing a rare night-blooming orchid for about forty years especially for the event. Despite the investment the flower dies shortly after its blooming. Aliceâs flight is delayed due to a thunderstorm forcing Dennis to stay at Mr Wilson's for the night of the orchidâs blooming. Martha is understanding, but George is deeply dismayed about this. But, at Martha's insistence, he eventually agrees to let Dennis stay outside for the party only with a firm warning to behave himself. Dennis does not enjoy the party much because the guests pinch his cheeks, and distances himself from the guests. However, in his curiosity, he finds himself pushing a button, which opens the garage door, causing it to knock over the dessert table and make a huge mess. Mr. Wilson sees the mess, he angrily bans Dennis from the party. From inside, Dennis hears Switchblade Sam robbing the house, goes downstairs, and finds Mr. Wilson's gold coins missing. Just as the flower is about to bloom, he alerts Mr. Wilson of the robbery, distracting everyone just long enough to miss the flower's brief blooming span. Furious about his forty year investment gone to waste and everything else, Mr. Wilson severely scolds Dennis, telling him that he does not want to see him or know him anymore and orders him out of his way, sending all the guests home. Dennis tries to apologize, and flees on his bike with a wagon attachted to it and he rides off into the night, he then heads into the park, where he eventually bumps into Switchblade Sam, who abducts him, intending to use him as a hostage.Dennis's parents Henry and Alice arrive home soon after only to learn of their son's absence. They then contact the authorities and his friends to begin searching for him. Mr. Wilson, now feeling intense guilt and remorse about what he had said, especially since he really had been robbed, joins in the search in his car, and everyone ends up searching for him all night. Meanwhile, Dennis unintentionally but effectively defeats Switchblade Sam by tying him up with rope, setting him on fire twice, accidentally bludgeoning him several times, and handcuffing him and losing the key amongst other things. He then returns to Mr. Wilson's house the next morning with an injured Switchblade Sam in his wagon, having also recovered Mr. Wilson's gold coins. Switchblade Sam is then taken into police custody by an amused sheriff who had advised him earlier to leave town. Dennis and Mr. Wilson make amends, and both the Mitchells and the Wilsons become close friends on better terms. That night, Alice told Mr &amp; Mrs Wilson that she does not have to travel out of town anymore and will stay to work on local projects and Dennis can come to work with her, since they have a daycare center. Mr. Wilson scoffs at this saying he and Martha are will be happy to continue watching Dennis, explaining that he's learned some things about children by saying to both Alice &amp; Henry that kids are kids and they have to play by their rules, roll with the punches and expect the unexpected. Around the same time, just as Dennis is still trying to get the flame out of his marshmallow, the marshmallow lands on Mr Wilson, accidentally hitting him in the forehead.As the closing credits begins to roll, Andrea, the egotistical co-worker of Dennis's mother finds him sitting near the copying machine as she's using it. He asks to the push the button on the copier, but she arrogantly tells him that he doesn't know what to do. Sure enough, he pushes the "PRINT" button and runs off with other workers, including Dennis's mother, looking on. Andrea gets her scarf sucked into the machine and her head gets pinned face down on the scanner bed and the machine relentlessly flashes its blinding light in her eyes and repeatedly copies her face and spews out page after page of black and white photos showing her various agonized facial expressions as she screams and cries on the scanner bed, eventually getting herself free.
Output: Question: What do Dennis' parents learn when they return home?, Answer: Their son was missing