So the Missionaries are kidnapped by the evil Burmese army and taken away.
The Pastor of the Church flies out to meet with Rambo personally and ask him to lead a group of mercenaries down the river to rescue the good guys. The mercenaries are led by Lewis, a typical Hollywood black-hearted English hooligan type character, School Boy (Michael Marsden), the stereotypical nice US buddy good-guy, and the others are not worth mentioning.
Rambo takes them down river to meet with a young guerrilla fighter/guide, who takes them to the village. They look on the carnage and are about to leave when an army truck shows up, and the bad guys are going to play their evil party games again. They throw some mines into a rice field, and make a few prisoners run through it.
Rambo has followed the mercenaries, and with his trusty bow takes out the soldiers.
Lewis is ready to leave, but prompted by Rambo sticking the bow in his face, and the others giving in to their conscience, they decide to complete the mission and rescue the missionaries.
Back at the army basecamp, the soldiers have forced some of the girls to dance for them, while those that dare look the commander in the eye are fed to the pigs. The missionaries are kept locked in cages.
Using the truck they have captured, Rambo's boys dive out one at a time into the village and take up their positions. They find and break out the missionaries, but Rambo sticks to the mission, and allows the Burmese commander to have his way with a small boy, which will infuriate you. The others rescue a few of the dancing girls, and they get back to the rendezvous point with all the missionaries except one - the girl.
Rambo gets to Sarah just in time to rescue her from one of the soldiers, who he kills by tearing out his voice box.
Rambo is late. Lewis refuses to wait and takes the others away to safety.
Rambo and Sarah get to the main gates but are surrounded by guards ... when suddenly School Boy comes to the rescue with his sniper rifile and takes out the soldiers (in style too!). They escape together.
In the morning, the soldiers discover their dead friends and the missing missionaries, and get out the dogs to give chase. Meanwhile Lewis steps on a mine and is missing a few limbs. Now the others must carry him.
Rambo splits from Sarah and School Boy, to throw the dogs off their scent. He makes a booby trap with their last mine strapped to the huge bomb they found earlier in the jungle. He sprints away to get out the of blast radius. The soldiers giving chase find the trap ... and are obliterated.
Lewis's team have reached the boat - but have been captured by the enemy commander and his remaining men. They are held at gunpoint. School Boy can only watch through his sniper rifle lens.
Suddenly Rambo pops up behind a soldier manning a machine gun turret, takes him out, and then turns it on the soldiers. Some of the soldiers manage to shoot back and Rambo is shot, but this doesn't slow him down. He turns the gun onto a gunboat that has showed up and destroys it. Even the lead missionary (24's Chappelle), must murder - and finally realises that Rambo was right all along and some evil people just do not play by the rules.
The Commander escapes into the jungle --- but is tracked by Rambo. Rambo pounces onto him, and slices him open, so his intestines spill to the ground in a grisly, but well-earned, death scene.
The missionaries finally have a chance to relax and enjoy their freedom.
Later, Rambo returns home to his farm and approaches the mailbox. Must be quite a few bills to catch up on.