After being wounded and near death, Harry Spikes, Ron Howard, an aging outlaw from the waning days of the Old West, is discovered and cared for by three young friends — Charles Martin Smith as Tod Hayhew, Lee Marvin as Harry Spikes himself, and Noah Beery Jr. as Basset. These boys, William "Wil" Young, Les Richter, and Tod Hayhew, are impressionable and eager for adventure. Despite their youth, they show kindness to Spikes without expecting any reward, refusing to accept payment for nursing him back to health. Jubilant that their good deed saved him, Spikes leaves them with a promise: that he won't forget their kindness, hinting at a possible future connection, even as he departs into the sunset.
Motivated by the stories of Spikes and driven by a desire for excitement, Wil, after suffering a harsh beating from his father Abel, begins to dream of a different life — one filled with adventure and the thrill of the outlaw lifestyle. With encouragement from Spikes's tales of the good old days, Wil makes the bold decision to run away from home, prompting Charles Martin Smith and Lee Marvin to join him. The trio travels to a small Texas town, hungry and feeling hopeless, where they formulate a daring plan to rob a bank. Their attempt, however, quickly turns tragic: Tod accidentally kills a man during the escape, and Les drops all the money they managed to steal, but despite these setbacks, they manage to flee across the border into Mexico, seeking refuge.
In the Mexican border town of Piedras Negras, the boys are left penniless and desperate. Wil sells his grandfather's antique watch for $10, just enough to buy them a meal. That night, they try to steal the watch back, but their plan goes awry, and they stumble directly into the sheriff’s office, landing them in jail. They spend eight weeks there, enduring hardships and despair until one day, they notice Spikes outside the window. Recognizing him, the boys call him over, and to their relief, Spikes, true to his word, bribes the jailer to release them, providing baths, food, and comfort. Before leaving, he reveals to them that the man they killed was a state senator, and now each of them has a bounty of $1500 on their heads, dead or alive.
Despite their criminal pursuits, the boys attempt to turn their lives around in Mexico, working various menial jobs and trying to stay out of trouble. However, their old life beckons when Spikes offers to take them into his gang. He tests their skills with a failed bank robbery in Mexico, but trouble escalates when they cross back into the United States. Inside a town, they are confronted by Billy Blanco, also known as Kid White, a seasoned old man who senses their plan and seeks to join their gang. Spikes, wary of him, turns him away, but Kid White attempts to prove himself by challenging the boys to a gunfight, which tragically results in the old man’s accidental death when Wil fires his gun.
From this point, everything spirals downward. The bank robbery, meant to be their big break, turns into a catastrophic failure: Tod is shot in the back, and they face a standoff with law enforcement. They are momentarily safe, but Spikes, realizing Tod is dying, urges the boys to abandon him and look out for themselves. Refusing to leave their friend behind, Wil and Les listen to Spikes, who then departs with the ominous words, “Good luck.” During their attempt to find medical help for Tod, Wil attracts the attention of the posse, and they are caught burying their friend.
Wil then makes his way back to Mexico alone, seeking to deliver a final message to Tod’s family, and promises to reunite with Les in the town of Piedras Negras in exactly two weeks, at the “Big Church.” When Wil finally returns, he finds that Les has been severely wounded—shot four times in an attack by bounty hunters named Morton and Spikes himself. In a tense confrontation, Wil kills Morton outside the infirmary but arrives too late to save Les. Les dies in Wil’s arms, leaving him devastated.
As the story reaches its climax, Wil heads to a hotel to face Spikes, who he believes is responsible for turning against them. Spikes, caught in a web of deals with the state governor of Texas, confesses that he has agreed to turn in the boys for a pardon, revealing that he met with officials and was promised immunity—if he delivered them. Spikes claims he had no choice when he shot Les, explaining, “I didn’t mean to kill him, I drew on him and had no choice.” Wil, furious and grieving, demands a fair fight, but Spikes draws a hidden gun, shooting Wil in the chest. Despite his wounds, Wil manages to fire back, killing Spikes just as he stumbles out of the hotel.
The movie concludes with Wil imagining himself boarding a train, dreaming of returning home to embrace his father and escape his turbulent life, but he succumbs to his injuries and collapses dead. The film ends with a nostalgic montage of the boys in their early days, echoing their last words: “C’mon, let’s go get lucky!” showcasing both the innocence and tragedy of their youthful adventure, as well as the harsh realities of their pursuits and losses.
