A young ne’er-do-well, Lightfoot (Jeff Bridges) steals a car. Elsewhere, an assassin attempts to shoot a preacher delivering a sermon at his pulpit. The preacher escapes on foot. Lightfoot, who happens to be driving by, inadvertently rescues the preacher by running over his pursuer and giving the preacher a lift.
Lightfoot eventually learns that the “minister” is really a notorious bank robber known as “The Thunderbolt” (Clint Eastwood) for his use of an Oerlikon 20 mm cannon to break into a safe. Hiding out in the guise of a clergyman following the robbery of a Montana bank, Thunderbolt is the only member of his old gang who knows where the loot is hidden.
After escaping another attempt on his life by two other men, Thunderbolt tells Lightfoot that the ones trying to kill him are members of his gang who mistakenly thought Thunderbolt had double-crossed them. He and Lightfoot journey to Warsaw, Montana to retrieve the money hidden in an old one-room schoolhouse. They discover the schoolhouse has been replaced by a brand-new school standing in its place.
Thunderbolt and Lightfoot are abducted by the men who were pursuing them—the vicious Red Leary (George Kennedy) and the gentle Eddie Goody (Geoffrey Lewis)—and driven to a remote location where Thunderbolt and Red fight each other, after which Thunderbolt explains how he never betrayed the gang.
Lightfoot proposes another heist—robbing the same company as before—with a variation on the original plan; the variation being due to Lightfoot inadvertently killing their electronics expert, Dunlop, the man who tried to assassinate Thunderbolt in the earlier scene. In the city where the bank is located, the men find jobs to raise money for needed equipment while they plan the heist.
The robbery begins as Thunderbolt and Red gain access to the building. Lightfoot, dressed as a woman, distracts the Western Union office’s security guard, deactivates the ensuing alarm, and is picked up by Goody. Using an anti-tank cannon to breach the vault’s wall, as they did in the first heist, the gang escapes with the loot. They flee in the car, with Red and Goody in the trunk, to a nearby drive-in movie in progress. Upon seeing a shirt tail protruding from the car’s trunk lid (which is a strong indication one or more people are hiding in the trunk to avoid paying), the suspicious theater manager goes to investigate. Red becomes increasingly agitated and Thunderbolt leaves the drive-in, encountering police at the exit. Thunderbolt tries to evade the police, and a chase ensues. Goody is shot and Red throws him out of the trunk onto a dirt road, where he dies.
Red then forces Thunderbolt and Lightfoot to stop the car. He pistol-whips them both, knocking them unconscious, and violently kicks Lightfoot in the head multiple times. Red takes off with the loot in the getaway car but is again pursued by police, who shoot Red several times, causing him to lose control of the car and crash through the window of a department store, where he is attacked and killed by the store’s vicious watchdog.
Escaping on foot, Thunderbolt and Lightfoot hitch a ride the next morning and are dropped off near Warsaw, Montana, where they stumble upon the one-room schoolhouse—now a historical monument on the side of a highway—moved there from its original location in Warsaw after the first heist. As the two men retrieve the stolen money, Lightfoot’s behavior becomes erratic as a result of the beating.
Thunderbolt buys a new Cadillac convertible with cash, something Lightfoot said he had always wanted to do, and picks up his waiting partner, who is gradually losing control of the left side of his body. As they drive away celebrating their success with cigars, Lightfoot, in obvious distress, tells Thunderbolt in a slurred voice how proud he is of their ‘accomplishments’, and slumps over dead.
Thunderbolt snaps his cigar in half (as it is no longer a celebration), and with his dead partner beside him, he drives off down the highway into the distance.