Big Jake begins in 1909 with John Fain and his outlaws raiding the McCandles’ family ranch. They kill the ranch hands, and kidnap Little Jake. Then head down to their hideout in Mexico, but not before dropping off a ransom note.
Both the army and the Texas Rangers offer Martha, the McCandle’s matriarch, their help in tracking down the gang. She’s only looking for extremely harsh and unpleasant kind of people to bring back her son. Instead, she asks her estranged husband, Jacob “Big Jake” McCandles for help. He’s older now, but still a legendary gunfighter out west…most people think he’s already dead.
After Jake arrives, the two discuss how to get the kidnappers their million dollars. They decide to put it in a big red strongbox. However, Jake warns that they still risk of never seeing their boy again.
Jake’s son, Michael rides up on his motorcycle, with word the kidnappers are in the Chilicothe Canyon. A Texas Ranger captain is there, and he offers his men for backup. However, the gang ambushes them, and they are taken out.
Jake is old school, and prefers to follow them on horseback, with his Apache friend, Sam Sharpnose, and his sons, Michael and James. Tensions are high with his boys over Jake’s deserting the family ten years earlier.
At night, Fain rides into the McCandles’ camp to arrange the handover. He tells Jake that they will send the boy’s body back in a basket if anything funny happens. The McCandles enters into Mexico the next day, and they check into a hotel. They are fully aware that another gang of men, with the intent of stealing the strongbox, is closely following. Jake sets a trap for them, and they kill all the men in that gang.
During the attack, the chest ripped open to reveal clipped bundles of newspaper instead of money. Michael and James, not trusting their father, fight Jake over it. He’s able to reassure them that it was both his AND Martha’s idea.
A thunderstorm rolls in, and the outlaw, Pop Dawson, arrives to give them the details of the exchange. He warns them that a sniper will always have his gun pointed on the boy if anything funny happens. Jake tells Michael to follow after them, and to take out that sniper.
Back at the hideout, Jake enters their lair alone. He finds Fain and four other gang members waiting. One of them holds a shotgun on Little Jake. The elder Jake tosses the key of the chest to Fain. He opens it up to discover there’s no real money in it.
Fain orders his brother, Will, to kill the boy, but Jake shoots him first. The sniper wounds Jake’s dog, and then hits Jake’s leg before Michael can take the sniper out himself. Jake orders his boy to run, but John Goodfellow, who just hacked Sam to death with his machete, is already after the little one.
Jake’s dog rescues Little Jake, but he dies saving the boy. Big Jake arrives, and impales Goodfellow to death on a pitchfork. Fain rides up to kill the two Jakes, but Michael ambushes him from his hiding place, and shoots him off his horse. As Fain dies, he’s surprised to learn Jacob McCandles is still alive. With Little Jake rescued, the McCandles head home.