Smiler Grogan, a freshly released convict, meets a tragic end when he crashes his vehicle on California State Route 74. As he takes his last breaths, Grogan shares a tantalizing secret with a group of concerned motorists: there is $350,000 (which would be about $3,594,728 in 2024) buried in Santa Rosita State Park, marked by the symbol of "a big W." However, when the group can't reach an agreement on how to split the fortune, they all scramble toward the park in a heated race.
Among those in a rush is Melville Crump, portrayed by Sid Caesar, who is enjoying a second honeymoon with his wife Monica. They charter a dilapidated biplane to Santa Rosita. Unfortunately, their arrival is hindered as they get trapped in the basement of a hardware store. In their desperate attempts to escape, they resort to dynamite, creating an explosive exit, and then hop into a cab to continue their journey to the park.
The duo of Ding Bell and Benjy Benjamin, played by Mickey Rooney, are making their way to Las Vegas when they also charter a small plane. Things take a chaotic turn when their inebriated pilot passes out, forcing them into a nail-biting scenario to safely land the plane. Once they manage to make it onto solid ground, they, too, hire a cab to reach their treasure destination.
Another key player in this frantic treasure hunt is J. Russell Finch, a businessman traveling with his wife Emmeline and her mother, Mrs. Marcus. Finch, played by Spencer Tracy, finds himself embroiled in a mishap when he crashes into a furniture truck driven by Lennie Pike. He enlists the help of British Army Lieutenant Colonel J. Algernon Hawthorne to drive them to Santa Rosita. A heated argument ensues, leading Mrs. Marcus and Emmeline to abandon Finch and Hawthorne in search of their own ride. The situation takes a wild turn when Hawthorne loses control of the vehicle while driving through a tunnel, resulting in chaos.
In a twist of fate, Pike finds motorist Otto Meyer, who becomes fixated on the prospect of the hidden money upon hearing about it. Greed takes over Meyer's resolve as he decides to pursue the treasure independently, leaving Pike behind and convincing a couple of service station attendants to detain him. When Pike finally breaks free by wreaking havoc at the station, he manages to steal a tow truck and later rescues Mrs. Marcus and Emmeline. Mrs. Marcus then makes a call to her son Sylvester, who misunderstands her instructions, causing further confusion. Eventually, this eclectic group finds their way back together and continues their wild quest to the park.
Meyer’s adventures lead him to assist a stranded miner in returning to his remote cabin. However, attempting to navigate back to the highway goes awry when he fails to cross a deep river, resulting in his car being swept away. In desperation, Meyer resorts to stealing yet another car to continue his pursuit.
Meanwhile, Santa Rosita Police Captain T. G. Culpeper is keen to resolve the Grogan case before he retires. He takes covert measures to shadow the frantic group of motorists as they embark on their escapades. Frustrated by his family tensions and with the grim realization that his pension is minuscule, Culpeper receives shattering news, sending him into a spiral of despair.
Ultimately, all fourteen adventurers converge at Santa Rosita nearly simultaneously, driven by the desire to find the "big W", which they soon realize is simply marked by a cluster of four palm trees. Culpeper arrives on the scene shortly after, observing the group as they unearth a suitcase full of cash. He reveals his identity as a police officer and encourages the group to surrender in hopes of receiving clemency for their misadventures.
However, the plot thickens as the group uncovers Culpeper’s ulterior motive—the officer intends to abscond with the money himself. A chaotic chase ensues through an abandoned structure that leads to a precarious fire escape. When the briefcase filled with cash bursts open, sending bills swirling through the air, Culpeper and the men find themselves scrambling for balance on a fire department ladder sent for rescue. The weight of their combined desperation causes the ladder to spin wildly, hurling them all off and leaving them catastrophically injured.
In the aftermath, while recuperating in a prison hospital, the men mourn the loss of their fortune and place the blame on Culpeper. He, in turn, laments his dwindling prospects, noting that due to the unforeseen loss of his pension and the further disintegration of family ties, he may never experience joy again. Just then, Mrs. Marcus, flanked by Emmeline and Monica, storms in to chastise the men only to slip on a banana peel and crash to the floor. The eruption of laughter that follows, except for Sylvester, somehow kicks off a moment of shared levity in the midst of their bleak situation, leaving even Culpeper unable to resist cracking a smile.
