Sam Whiskey (Burt Reynolds), an adventurer and rogue in the Old West, is seduced by widow Laura Breckenridge (Angie Dickinson) into promising to retrieve $250,000 in gold bars from a riverboat that sank in Colorado’s Platte River. The gold had been stolen by Laura’s late husband from the Denver Mint and replaced by plated lead fakes. She offers Sam $20,000 to recover and return it before the theft is discovered and her family name is ruined. Sam enlists the help of Jedidiah Hooker (Ossie Davis), a local blacksmith, and O. W. Bandy (Clint Walker), an Army friend turned inventor, offering them shares of the reward.
They locate the sunken riverboat, unaware that they are being watched by Fat Henry Hobson (Rick Davis) and his gang. The gold is fifteen feet below the river’s surface, so Bandy fashions a diving helmet for Sam out of a bucket and bellows, but Fat Henry and his gang capture Jed and Bandy. Thinking they have drowned Sam, hiding in the riverboat’s smokestack, they recover the gold and prepare to kill their captives. With the help of one of Bandy’s homemade machine guns, Sam frees his partners and they start for Denver with the gold. Just as they are tempted at a crossroads to head for Mexico with their haul, Laura shows up to greet them.
Assuming the identity of a government inspector, Sam enters the mint and deliberately damages a gold-plated bronze bust of George Washington displayed in the lobby. He then insists on having it repaired and takes it to a blacksmith’s shop, where Jed makes a mold of the bust and recasts the recovered gold. Fat Henry later breaks into the shop and steals the bronze original, thinking that it was made by Sam and his men to disguise the pilfered bars. Sam returns the new bust to the mint, and his men, posing as plumbers, conceal themselves until nightfall when they meltdown the bust and recast it into gold bars. On a train leaving Denver the next morning, Sam splits the $20,000 with Jed and Bandy but keeps Laura for himself.