Smiler Grogan, a recently released convict, crashes his car on California State Route 74. With his dying breath, Grogan tells a group of motorists who stop to help him about $350,000 (equivalent to $3,483,261 in 2023) buried in Santa Rosita State Park under “a big W.” Failing to negotiate a satisfactory way to split the money, the four cars begin a mad dash to the park, having several mishaps along the way:

Melville Crump, a dentist on a second honeymoon with his wife Monica, charters a rickety biplane to Santa Rosita. Despite arriving in Santa Rosita first, they get locked in a hardware store’s basement. After several attempts to break out, they blow out the wall of the basement with dynamite, and hire a cab to get to the park.
Ding Bell and Benjy Benjamin, two friends on their way to Las Vegas, charter a small airplane. When their alcoholic pilot knocks himself out, they struggle to land the plane themselves; once on the ground, they also hire a cab to get to the park.
J. Russell Finch, a businessman traveling with his wife Emmeline and her mother Mrs. Marcus, crashes into the furniture truck of Lennie Pike, another witness of Grogan’s crash. Finch persuades British Army Lieutenant Colonel J. Algernon Hawthorne to drive them to Santa Rosita. After a nasty argument, Mrs. Marcus and Emmeline exit the car to hitch their own ride. Hawthorne crashes the car while driving through a tunnel, and he and Finch come to blows.
Pike stops motorist Otto Meyer for a ride and tells him about the money; the greedy Meyer decides to search for the treasure himself, and abandons Pike, convincing two service station attendants to detain him. Pike destroys the station, steals a tow truck, and picks up Mrs. Marcus and Emmeline. Mrs. Marcus calls her son Sylvester, who lives close to Santa Rosita, but he misunderstands and drives to meet her. Eventually, the group reunites with Russell and Hawthorne, and continues to head to the park.
Meyer stops to help a stranded miner get back to his very rural cabin. Trying to get back to the highway, Meyer fails at crossing a deep river and his car is swept away, leading him to steal another motorist’s car.
Meanwhile, Santa Rosita Police Captain T. G. Culpeper, hoping to tie up the Grogan case before his impending retirement, secretly has the motorists shadowed throughout their various adventures. After a furious argument with his wife and daughter, Culpeper learns that his pension will be a pittance and has a mental breakdown.

The entire group, now consisting of fourteen people, arrives at Santa Rosita at nearly the same time, and searches frantically for the “big W”, which turns out to be a gathering of four palm trees. Culpeper arrives shortly after and observes the group. After the group digs up a suitcase full of cash, Culpeper identifies himself and informs the group that they are wanted by the police. He convinces them to turn themselves in and hope for leniency.

The motorists realize that Culpeper is not returning to the police station with them, but is stealing the money for himself. The men chase him into an abandoned building and onto a rickety fire escape, which starts to collapse under them. The briefcase containing the money falls open, scattering the cash to the wind. When Culpeper and the men all pile onto a fire department ladder sent to rescue them, their combined weight causes it to spin uncontrollably and fling them all off, leaving them heavily injured.

In the prison hospital, the men bemoan the loss of the money and blame their injuries on Culpeper, who responds that due to his lost pension (which his boss had successfully negotiated back, thus making his illegal actions unnecessary), the ruined relationship with his family, and the likelihood that the judge will probably give him the harshest sentence, he may never laugh again. Mrs. Marcus, flanked by Emmeline and Monica, enters and begins berating the men, only for her to slip on a banana peel and fall. All the men except Sylvester roar with laughter, and, after a brief hesitation, Culpeper joins in.