The movie tells the story of a soldier’s journey to locate a disaffected and unstable Colonel—played by a bald Marlon Brando in a brief appearance—who has retreated into the jungle, creating problems. The specifics of what he did are hazy, though it was evidently significant enough to warrant an expedition downriver to find him. The protagonist sets off with his unit to track down this eccentric figure before things escalate further. Robert Duvall provides some comic relief as a soldier seemingly unaffected by the war—particularly when a shell detonates nearby and he responds with a detached look. That was funny! However, generally speaking, it’s a slow-moving experience; I felt the film drifted without much to hold my attention.

Source on TMDB