In 1969, during the Vietnam War, United States Army Special Forces Colonel Walter E. Kurtz is deemed insane and now commands his own Montagnard troops, inside neutral Cambodia, as a demi-god. Colonel Lucas and General Corman, increasingly concerned with Kurtz’s vigilante operations, assign MACV-SOG Captain Benjamin L. Willard to “terminate” Kurtz “with extreme prejudice”.
Willard, initially ambivalent, joins a United States Navy river patrol boat (PBR) commanded by Chief, with crewmen Lance, “Chef”, and “Mr. Clean” to head upriver. They rendezvous with surfing enthusiast Lieutenant Colonel Bill Kilgore, 1st Cavalry commander, to discuss going up the Nùng. Kilgore scoffs, but befriends Lance after discovering he is a famous surfer and agrees to escort them through the Nùng’s Viet Cong–held coastal mouth. They successfully raid at dawn, with Kilgore ordering a napalm strike on the local cadres. Willard gathers his men to the PBR and journeys upriver.
Tension arises as Willard believes himself in command of the PBR while Chief prioritizes other objectives over Willard’s. Slowly making their way upriver, Willard reveals his mission partially to the Chief to assuage his concerns about why his mission should proceed. As night falls, the PBR reaches the American Do Lung Bridge outpost on the Nùng River. Willard and Lance enter seeking information for what is upriver. Unable to find the commander, Willard orders the Chief to continue as an unseen enemy launches an assault on the bridge.
The next day, Willard learns from dispatch that another MACV-SOG operative, Captain Colby, who was sent on an earlier mission identical to Willard’s, had joined Kurtz.a Meanwhile, as the crew read letters from home, Lance activates a smoke grenade, attracting the attention of a camouflaged enemy, and Mr. Clean is killed. Further upriver, Chief is impaled by a spear thrown by the natives and attempts to kill Willard by impaling him. Willard suffocates him, and Lance buries Chief in the river. Willard reveals his mission to Chef, but despite his anger towards the mission, he rejects Willard’s offer for him to continue alone and insists that they complete the mission together.
The PBR arrives at Kurtz’s outpost and the surviving crew are met by an American freelance photojournalist, who manically praises Kurtz’s genius. As they wander through they come across a near-catatonic Colby, along with other US servicemen now in Kurtz’s renegade army. Returning to the PBR, Willard later takes Lance with him, leaving Chef behind with orders to call in an airstrike on Kurtz’s compound if they do not return. Chef is later killed by Kurtz.
In the camp, Willard is subdued, bound, and brought before Kurtz in a darkened temple. Tortured and imprisoned for several days, Willard is released and allowed to freely roam the compound. Kurtz lectures him on his theories of war, the human condition, and civilization while praising the ruthlessness and dedication of the Viet Cong. Kurtz discusses his family, and asks that Willard tell his son about him after his death.
That night, as the Montagnards ceremonially slaughter a water buffalo, Willard stealthily enters Kurtz’s chamber, as he is making a recording, and attacks him with a machete. Mortally wounded, Kurtz utters “…The horror … the horror …” and dies. All in the compound see Willard departing, carrying a collection of Kurtz’s writings, and bow down to him. Willard then leads Lance to the boat and the duo motor away. Kurtz’s final words echo eerily as everything fades to black.