It's a Mad, Mad, Mad, Mad World

Smiler Grogan, recently released from prison, crashes his car on California State Route 74. With his dying breath, he reveals to nearby motorists that $350,000 is buried in Santa Rosita State Park under 'a big W.'

Following Grogan's shocking revelation, several motorists begin to argue over how to share the found treasure. Unable to reach an agreement, they hastily decide to race to Santa Rosita in a bid to find the money themselves.

Melville Crump, a dentist on a second honeymoon with his wife Monica, charter a rickety biplane to reach Santa Rosita. Upon their arrival, they find themselves locked in a hardware store's basement, leading to a desperate attempt to escape rather than search for treasure.

Ding Bell and Benjy Benjamin, two friends heading to Las Vegas, board a small airplane. Their flight goes awry when their intoxicated pilot loses consciousness, forcing them to land the plane themselves as they race towards Santa Rosita.

J. Russell Finch, traveling with his wife Emmeline and her mother Mrs. Marcus, crashes into Lennie Pike's furniture truck. After the accident, Finch manages to convince Colonel J. Algernon Hawthorne to drive them to Santa Rosita, leading to conflict within the group.

During their chaotic travels, Mrs. Marcus and Emmeline depart from Finch and Hawthorne’s car to hitch a ride themselves. Meanwhile, Lennie Pike, aiming for the treasure, persuades Otto Meyer to give him a ride but ends up being abandoned as Meyer plots to find the money.

Otto Meyer, trying to reach the treasure, stops to help a stranded miner. However, his attempts to cross a deep river result in him losing his car to the current, leading to desperate measures as he resorts to stealing another motorist's vehicle to continue his quest.

Santa Rosita Police Captain T. G. Culpeper, eager to close the Grogan case before retirement, is overwhelmed by personal issues. Following a heated argument with his family, he suffers a mental breakdown while monitoring the activities of the motorists seeking the treasure.

All fourteen motorists arrive at Santa Rosita nearly simultaneously and split up to search for the 'big W.' After much confusion, they discover that the treasure is buried beneath a group of four palm trees and dig up a suitcase overflowing with cash.

After the motorists unearth the suitcase, Culpeper shows up, identifying himself as a police officer. He convinces them to turn themselves in by promising leniency, but secretly plots to keep the money for himself.

As the plot unfolds, the motorists realize Culpeper's true intentions and pursue him into an abandoned building. A chase ensues onto a rickety fire escape, leading to a catastrophic event where all parties end up injured when the escape collapses.

The men, now in a prison hospital, complain about the loss of the money and their injuries, blaming Culpeper. As they wallow in misery, Culpeper explains his bleak future due to the consequences of his actions, revealing a deep sense of regret.

Mrs. Marcus, alongside Emmeline and Monica, storm into the hospital only to chastise the men for their involvement in the debacle. However, her grand entrance takes a comedic turn as she slips on a banana peel, leading to unexpected laughter from the injured men.

In a moment of absurdity, the men burst into laughter following Mrs. Marcus's fall, finding humor in their dire situation. Even Culpeper joins in, suggesting a sense of camaraderie despite their grim circumstances.