In the Old West, the five richest men in the territory gather in Laredo for their annual high-stakes poker game, where pride and risk ride high with every raise. When undertaker Benson Tropp, Charles Bickford, calls them to order in his horse-drawn hearse, the tension grows as cattleman Henry Drummond, Jason Robards pressures a postponement of his daughter's wedding, while lawyer Otto Habershaw, Kevin McCarthy abandons his closing arguments in a life-or-death trial. They are joined by Dennis Wilcox, Robert Middleton, and Jesse Buford, John Qualen, in the back room of Sam's saloon, as curious townsfolk linger outside, waiting for any word from the table.
Settler Meredith, Henry Fonda his wife Mary, Joanne Woodward, and their young son Jackie, Jean-Michel Michenaud are passing through on their way to buy a farm near San Antonio when a wagon wheel breaks. They wait at Sam's while the local blacksmith tends to the repairs. Meredith, a recovering gambler, learns of the big game and asks Habershaw if he can watch. Struck by Mary’s look, Habershaw invites Meredith to the table, and Meredith eventually bets all of his family savings, the money meant to buy a home, on the outcome of the hand.
The game builds to a climactic hand; the pot swells to more than $20,000 as the players push and pull, risking everything. Meredith, short on cash, can’t call the latest raise. Under the strain, he collapses. The town physician, Doc Scully, is called to care for the stricken man. Barely conscious, Meredith signals for his wife to stay in the room and play out the hand. Taking his seat, Mary asks, > "How do you play this game?" < The others howl in protest, but they eventually concede and let her proceed.
The situation is explained to her: if she cannot match the last raise (and any subsequent ones), she will be out of the hand. Despite the men’s protests, she leaves the room to borrow additional funds. With Jackie and four of the players trailing behind, Mary crosses the street to speak with the owner of the Cattle and Merchants' Bank, C. P. Ballinger. After she shows him her hand, Ballinger suggests she is playing a practical joke. When he is told otherwise, he lends her $5,500 (at 6% interest) and makes a $5,000 raise for her. The other players, aware of Ballinger’s cautious nature, fold one by one. Mary collects a sizable winnings and repays Ballinger with interest. The game ends without anyone seeing the winning hand.
The woman’s resolve earns her the admiration of the men. Drummond is so moved that, upon returning to the wedding ceremony, he speaks privately to his prospective son-in-law, slips him some money, and urges him to run away and find a better wife.
In the end, Meredith, Mary, and their “son” are revealed to be confident tricksters and expert card sharps. With the help of Scully—who dreams of romance far from the tedium and poverty of a country doctor’s life—and at Ballinger’s behest, they have schemed against the other poker players, who themselves had swindled the banker in a real-estate deal 16 years before. “Mary” is actually Ballinger’s mistress, Ruby. She promises to give up gambling after the caper, but she sits down to another poker game, much to Ballinger’s dismay.
