Richard "Richie" Rich Jr. (Macaulay Culkin) is the world's wealthiest kid, the son of Imagineer and philanthropist Richard Rich, Sr. (Edward Herrmann), worth $70,000,000,001. Richie has loyal butler Herbert Cadbury (Jonathan Hyde) as a companion. He lacks any friends his own age. But he thinks he might get his chance at a dedication to the reopening of United Tool, a factory Richard recently acquired (intending to modernize the factory and give it away to the workers as a token of goodwill). There Richie encounters a group of sandlot kids playing baseball. Unfortunately, the too-strict head of security, Ferguson (Chelcie Ross), stops Richie and pulls him sharply away. Cadbury warns Ferguson against being too rough with Richie.Richard tries to keep in touch with Richie and spend time with his son whenever he can. He even had the Rich family's head scientist, Professor Keenbean (Michael McShane), invent a machine called the "Dadlink" that pinpoints Richard's location in seconds, so Richie can talk to his dad whenever he's away on business. Meanwhile, the greedy CFO of Rich Industries, Laurence Van Dough, is planning to steal the Rich financial fortune, believed to be stored in the Rich family vault. Van Dough, with the help of Ferguson, plots to blow up the plane (a Douglas DC-3 christened the Billion Dollar One) carrying the Rich family to England by disguising a bomb among the presents that they were to give to Queen Elizabeth II. Cadbury, seeing Richie's loneliness, makes a suggestion to Richie's mother, Regina, and arranges for Richie to stay home in Chicago with the sandlot kids for a weekend of fun. That weekend allows Richie to earn the friendship of the sandlot kids.Thanks to the new invention of Professor Keenbean, the Smellmaster 9000 which translates smell into sound, the bomb is detected. Richard is able toss the bomb out his window, but it detonates, destroying part of the tail, sending Billion Dollar One into the Atlantic Ocean. Richie Sr. and Regina survive the crash and climb into one of the plane's inflatable rafts. Believing that Richie's parents are dead, Van Dough assumes leadership of the Rich corporation, and proceeds to cut the many charitable contributions the Rich family were known for. This includes closing the recently reopened United Tool factory, which the parents of the sandlot kids relied upon for their living. This angers Richie, who proceeds to the company headquarters and, as a living Rich family member, assumes the leadership position.Van Dough, however, saw this as a minor setback: as Richie is still underage, his ability to run the business was limited by the powers to him by someone who was able to give it to him - namely, Cadbury. Cadbury is framed for the Rich family's murder, and the Rich family's other loyal servants are all fired together by Van Dough's edict, effectively isolating Richie from the outside world and making him a prisoner within his own home. However, he does get the assistance of Keenbean, who has been distrustful of Van Dough from the start. Hiding in his lab, located in the basement of Rich Manor, Keenbean listens in on Van Dough and Ferguson playing pool.They plot to have Cadbury murdered and appear to have committed suicide. The professor manages to sneak Richie out with a plan to break Cadbury escape from prison. After Cadbury gets the supplies (a card in Latin, a language he is fluent in, to warn him and Keenbean's mixture, which will eat through literally anything), he is attacked by one of Van Dough's henchmen; surprisingly, he shows great strength for his appearance, and knocks the goon unconscious. Dressing in the goon's leather and denim biker clothes, Cadbury then regroups with Richie, his new friends and one's mother (whom Cadbury is falling for). They are willing to assist Richie in whatever it takes to get his home back.During this time, Van Dough finds out about Cadbury's escape and, with Ferguson's help, confronts Keenbean. They tie the professor up and threaten to throw him into his molecular Reorganizer, which turns garbage into whatever's typed in (a bedpan in this case), unless he gets them into the vault. Keenbean states the lock is voice-activated and only Richard and Regina can open it.Meanwhile, Richie was left with the Dadlink. However, Richard's receiver was broken in the crash, and when Richard manages to fix it, the signal is intercepted by Ferguson, who disconnects Richie's modem from the phone line, leaving Richie (remoting in from a friend's terminal) in the dark as to where his parents may be. After rescuing Keenbean from captivity, the kids manage to sneak Richie back into Rich Manor, only to discover that the Dadlink shows that Richie's parents are inside the Rich's house. He is shocked to discover that Van Dough had anticipated his own arrival and had arranged for his parents' rescue. Held at gunpoint, Van Dough forces the Rich family elders to the Rich vault, while Ferguson and his men take Richie and his friends to the molecular Reorganizer. Using his ultra-adhesive substance Cementia and his remote-controlled RoboBee, Keenbean thwarts Ferguson's plan and manages to save Richie and his friends. Richie then proceeds to take a bag full of Keenbean's inventions in a bid to save his parents.Van Dough is eventually led to Mount Richmore, a stone mountain portrait of the Rich family, where the vault is located. There, he is furious upon discovering that the vault holds the Rich family's childhood memories and treasures - nothing that was valuable to him. Demanding an explanation, he finds the Rich family keeps their money in banks, the stock market, and real estate, because they simply do not value money. Desperate to get the money, he attempts to shoot Richard and Regina, only for Richie to interfere. Van Dough attempts to shoot Richie instead, but manages to barely faze him, his clothes having turned bulletproof thanks to one of Keenbean's inventions.The Rich family then takes the opening caused by Keenbean's invention to escape. The chase eventually leads them down the side of the mountain, where they are under further attack by Ferguson (covered in pieces of towel from the Cementia) and a special rock-blasting laser that had been used to sculpt the mountain vault. Cadbury finally manages to disarm Ferguson and manages to keep the Rich family safe, while Van Dough hangs upside down for dear life, after Cadbury fires at him. Although Richard abhors firing staff, he allows Richie to fire Van Dough, who is then subsequently decked by Regina and arrested.Later, Richie plays baseball with his new friends for the United Tool team on Rich Manor's yard (with Cadbury as team coach and Keenbean as umpire) and hits a home run that's picked up by Van Dough, who's doing gardening with Ferguson as work release.