This movie was based on the novel by Joseph Conrad entitled "Heart of Darkness" and is a longer version of the original.
US Army Captain, and CIA operative, Cpt Willard (Martin Sheen) has been assigned to infiltrate renegade special forces, Colonel Kurtz's, (Marlon Brando) troops and terminate the Colonel's command by death in Cambodia during the Vietnam war..
As Willard descends into the jungle he is slowly over taken by the jungles mesmerizing powers and the battles and insanity which surround him.
His team soon begin to succumb to drugs and are slowly killed off one by one. As Willard continues his journey he begins to realise he is becoming more and more like the man he was sent to kill.