The film opens on October 6 1971. Jacob Singer (Tim Robbins) is a U.S. soldier in the Mekong Delta, Vietnam. Helicopters pass overhead, carrying supplies for what appears to be preparation for a big Viet Cong offensive. Without any warning, Jacob's unit comes under fire. The soldiers try to take cover, but begin to exhibit strange behavior for no apparent reason. Jacob tries to escape the unexplained insanity, only to be bayonetted by an unseen enemy.
The film shifts between Vietnam, to Jacob's memories (and delusions) of his son Gabe (Macaulay Culkin, uncredited) and former wife Sarah (Patricia Kalember), to his present (this timeframe is set in 1977) relationship with a woman named Jezebel (Elizabeth Peña) in New York City. During this time, Jacob faces several threats to his life and has severe hallucinatory experiences. It is revealed that his son Gabe was hit by a car and killed while Jacob was in Vietnam.
Jacob's friend and chiropractor Louis (Danny Aiello) states the main thematic point of the film: in effect, hell is really purgatory, and those who are ready to let go of their lives do not find the experience 'hellish'. It is at this point in the movie that Louis cites the 14th century Christian mystic Meister Eckhart.
As the hallucinations become increasingly bizarre, Jacob learns about chemical experiments performed on U.S. soldiers in Vietnam. His surviving platoon-mates confess to Jacob that they have been seeing horrible hallucinations as well. Jacob loses an army buddy in a car-ignition explosion while reaching down to pick up a quarter. Jacob is then approached by a man named Michael Newman (Matt Craven), who claims to have been a chemist working with the Army's chemical warfare division in Saigon where he worked on creating a drug that would increase aggression in soldiers. Tests of the drug (code-named "The Ladder" in reference to the effect) were first given to monkeys and then to a group of enemy POWs, with gruesome results. Later small doses of "The Ladder" were given to Jacob's unit, through the platoons' C-rations. However, instead of targeting the enemy, the men in Jacob's unit attacked each other indiscriminately.
We finally learn that Jacob never made it out of Vietnam; the entire series of experiences turns out to have been a dying hallucination. Jacob's experiences appear to have been a form of purgation in which he releases himself from his earthly attachments, finally joining his dead son Gabe to ascend a staircase toward a bright light.
At the end of the film, a message is displayed mentioning the testing of a drug named BZ, NATO code for a deliriant and hallucinogen known as 3-quinuclidinyl benzilate that was rumored to have been administered to U.S. troops by the government in a secret attempt to increase their fighting power. The effects of BZ, however, are different from the effects of the drug depicted in the film.
Director Adrian Lyne uses a body horror technique in which an actor is recorded waving his head around at a low frame rate, resulting in horrific fast motion when played back. Filmmakers have since achieved the effect by digitally removing frames from footage shot at a normal rate.
The horror videogame franchise Silent Hill borrows this technique in the second, third and fourth sequels of the game, although it is not seen in the Silent Hill movie. Other films to use the "fast-head" motion include Stir of Echoes, Austin Powers: International Man of Mystery, The Ring, Oldboy, Trauma (2004), House on Haunted Hill (1999), Lost Highway, Lost Souls, The Amityville Horror (2005), The Deaths of Ian Stone, and the Saw series, as well as the videogame Thief: Deadly Shadows.
The effect also appears in an episode of the television series Supernatural and in the The X-Files episode "Requiem". The music video for "Stupify" by Disturbed, the Linkin Park song "Papercut", "Payback" by Flaw, Marilyn Manson's cover of "Personal Jesus", "UHF" by Weird Al Yankovic and "Sober" by Tool also use the technique.