Harry Spikes (Lee Marvin) is an aging bank robber of the fading Old West. Injured and near death, he is found and mended back to health by three impressionable youths who are lifelong friends—Wil (Gary Grimes), Tod (Charles Martin Smith), and Les (Ron Howard). They refuse any payment from Spikes for their efforts, and when he’s healed he leaves saying he won’t forget their kindness. Later, after enduring a beating from his father, and encouraged by Spikes’s reminiscences of the good life, Wil decides to run away from home seeking excitement and easy living, and the other 2 boys decide to follow.
The three boys eventually make it to a Texas town, hungry and despondent, and in a moment of inspiration attempt to rob a bank. In the process Tod accidentally kills a man, and Les drops all the money, but they manage to escape and cross the Rio Grande into Mexico. Arriving in the Mexican town of Piedras Negras penniless and unable to find any work, Wil pawns his grandfathers antique watch for $10, enough to buy them a meal. That night, they attempt to steal the watch back, but stumble right into the sheriffs office, and land in jail.
After suffering in jail for 8 weeks, they happen to glance out the window and see Spikes and call him over. Good to his word, Spikes bribes the jailer, buys them baths, food and drink before saying his goodbye. He also tells them the man they killed was a state senator, and they now each have a bounty of $1500 on them, dead or alive. The boys stay in Mexico and attempt to go ‘straight’ working a succession of menial jobs, before again coming across Spikes who offers to take them into his “gang.”
They plan a bank robbery back in the US, with Spikes first testing their mettle on a dry run in the Mexican bank. Crossing the border they camp out outside the town and are come upon by an old man who has deduced their plan and wants into the gang. When Spikes tells him no, he attempts to badger the boys into a gunfight to prove his worth, and Wil accidentally shoots him dead. Everything begins to take a turn for the worse: the bank robbery is a colossal failure, Tod is shot in the back, and they have a shootout with the Posse. Momentarily safe, Spikes knows Tod is dying and encourages the others to abandon him and look out for themselves. Wil and Les refuse and Spikes leaves them, saying “Good luck.” Attempting to find a doctor, Wil attracts another Posse, who descend on them as they finish burying Tod.
After riding back to Mexico, Wil leaves Les as he wants to deliver a final letter to Tod’s family, saying he will meetup with Les in the “Big Church” back in the Mexican town of Piedras Negras in exactly two weeks. Arriving back from the journey, Wil enters the church and encounters a man who says Les sent him, and that he’s been sorely wounded, shot four times by 2 men, bounty hunters by the name of Morton and Spikes. Killing Morton outside the infirmary, Wil attempts to leave with Les only to have him die in his arms.
He heads to the Hotel to confront Spikes, and appears to surprise him in his hotel room with his gun still hanging on the bed post. Spikes tells him he met with the Governor of Texas himself, who promised him a pardon for all his crimes if he brings in the boys. He then says he respects Wil, and wishes it didn’t have to be the way it is, saying he didn’t mean to kill Les, but he drew on him and had no choice. Wil demands he stand up so he can kill him “fair,” but Spikes throws his hat at him and pulls a hidden gun, shooting him in the chest. However, Wil manages to get off a succession of shots and kill Spikes, before stumbling out of the hotel and to the train station. Wil imagines boarding the train and returning home to embrace his father, before he collapses dead.
The film ends with a montage of the boys when they first set out on the adventure, saying “C’mon, Let’s go get lucky!”