In the aftermath of the quirky game inventor Milton Parker's (Vincent Price) demise, his avaricious and estranged relatives flock to his sprawling mansion for the reading of his will. To their surprise, Charles Bernstein (Robert Morley), the deceased patriarch's lawyer, reveals an unusual stipulation: to inherit Parker's immense $200 million estate, the family must participate in a high-stakes scavenger hunt. This revelation sets the stage for an uproarious adventure as five competing teams are formed, each eager to seize the fortune.
Equipped with a puzzling list, each team is tasked with finding 100 diverse items that carry varying point values—ranging from a paltry 5 points to an impressive 100. The challenge? They must collect these items using any method they can conjure, other than purchasing them, and deposit their finds into one of five designated pens on the estate before the 5 p.m. deadline. The team that accumulates the highest score will emerge victorious.
As the scavengers swarm the Parker mansion, pandemonium ensues under the vigilant gaze of Bernstein and the scorekeeper Cornfeld. The escapades of Mildred, Stuart, and Georgie take them on a crazy thrill ride, which includes a daring toy bear heist from a local carnival, a brazen safe break-in at Stuart's office, and the outlandish theft of a Native American's false teeth. Stuart's misadventures further embroil him in trouble when he crosses paths with a motorcycle gang led by the infamous Scum (Meat Loaf), all while attempting to snag a fox tail from one of their bikes.
On another front, the group's servants embark on their own mischief-laden journey that entangles them in stealing a toilet from an uptown hotel, executing a convenience store heist for a cash register, and an ill-fated break-in at a laboratory to procure a microscope. Meanwhile, the antics of Kenny, Jeff, and Lisa involve "borrowing" various bizarre items, such as the head of Jack from a Jack in the Box, engaging a heavyweight ally in Duane, albeit briefly, and snagging a bulletproof vest from self-defense aficionado Arvilla (Ruth Gordon). Their escapade takes a comical turn when they accidentally get trapped in a football team's locker room while attempting to swipe a helmet.
Amidst all the chaos, Dummittz's quest for a Rolls-Royce grill results in an absurd series of events that finds him repeatedly run over in misguided attempts at replicating an insurance scam he once witnessed. His journey takes a wacky twist when he gets caught by Sam, a sharp-eyed security guard at a bridal shop, while trying to pilfer a pristine wedding gown. In a strange twist, the two form an unexpected partnership, conspiring to steal a suit of armor from a museum—Dummittz disguised as a mummy and Sam donning knightly armor. The adventure takes a wild turn when Sam is unexpectedly knocked out and whisked away by the cunning Mildred, Stuart, and Georgie.
Meanwhile, Motley's intention to impress his children sends him spiraling into a realm of absurdity, filled with outrageous attempts to procure peculiar items like a beehive, a life preserver, and a parachute. His hilariously inept attempts to steal a medicine ball from a gym and earn the favor of instructor Lars (Arnold Schwarzenegger) ultimately end in calamity, as he tumbles through a second-story window in his bumbling enthusiasm.
As the tension mounts, all three teams find themselves converging on San Diego Zoo, where they orchestrate a daring heist, absconding with an unsuspecting ostrich, much to the chagrin of beleaguered zookeeper Avery Schreiber. The ensuing bedlam escalates into a high-speed car chase back to the Parker mansion.
In a heartwarming culmination of teamwork, the remaining teams set aside their individual ambitions to assist Kenny, Jeff, and Lisa in their final showdown against the conniving Mildred, Stuart, and Georgie team. With mere moments to spare, Sam reawakens from his armor-clad daze and slides into the winning pen, securing the competition for the brothers and Lisa. In the end, this triumphant trio chooses to share their newfound fortune with the community, while the defeated Mildred, Stuart, and Georgie find themselves fleeing from an irate Native American, in pursuit of his missing dentures.
