Rambo is a disillusioned Vietnam vet who wanders from one place to another. He finds out a friend & fellow soldier has passed from his exposure to Agent Orange.
He goes to one Washington town where he is picked up by the sheriff who tells him "his kind" is not welcomed there & drops him off outside of town.
Tired of being pushed around, Rambo walks back into town where he is arrested by the sheriff & taken to jail where he is abused by the sadistic guards.
Having flashbacks from when he was a POW, Rambo escapes from jail & steals a motorcycle. The cops, including the sheriff, pursue him & corner him in the woods.
He takes down all the cops & warns the sheriff NOT to push him, telling him if he wants a war he'll give him one.
The sheriff, of course, doesn't heed Rambo's warning & continues pursuing him along with the National Guard where they corner him in a mine.
Soon Rambo's former commanding officer Col. Trautman shows up to join in the pursuit of Rambo.
He, too, warns the sheriff to back off chasing Rambo, saying how he's facing an "expert" in guerilla warfare.
Trautman contacts Rambo via radio to try to bring him in. Rambo refuses, saying to his former C.O.: "They drew first blood. Not me!"
Afterwards, Rambo has a firefight with the National Guard where they shoot a rocket into the mine. The rocket explodes & collapses the mine.
Everyone at first believes Rambo is dead, which angers the sheriff who wanted to kill him himself.
But Rambo survives the blast where he proceeds to wreak havoc on the town. He & the sheriff have a brief shootout. Rambo ends up wounding the sheriff.
Col. Trautman shows up & stops Rambo from killing him. He asks him what's wrong & Rambo tells him of the difficulties he's had since coming back from Vietnam.
In the end, Trautman convinces Rambo to turn himself in & Rambo is led away by police.
Just in time for the sequels!