Constantine

The film opens in a ruin in Mexico, where a young man finds the Spear of Destiny wrapped in a Nazi flag. This historical artifact was allegedly used by Roman soldier Longinus to pierce the side of Christ on the Cross. The character seizes the spearpoint and becomes possessed, heading for Los Angeles.

In Los Angeles we see John Constantine (Keanu Reeves) perform an exorcism on a teenage Filipino girl; although he is successful, he is unnerved by the boldness of the demon, who attempted to leave the girl's body to cross over into humankind's realm. After meeting a detective named Angela Dodson (Rachel Weisz), who wants to know if her twin sister committed suicide, John uncovers a plot by Mammon, the son of Satan, to betray his father and claim dominion over Earth immediately.

There are many worlds, according to Constantine, of which Earth is only one; it is a neutral place between Heaven and Hell. Apparently, God and Satan wagered on which can win the most souls among humans. Eschewing direct intervention as part of the bet, angels and demons cannot exist in the Earth plane; Instead, they interfere with humans by using what John refers to as "half-breeds," not fully angelic or demonic in form — though the movie gives no indication as to whether they are actually half-human in any meaningful sense. Some humans are able to see the half-breeds that walk among them. Having lived with this ability since birth, Constantine was institutionalized as an adolescent and eventually committed suicide to escape the torment of seeing them but not being believed. Though resuscitated by doctors, he was officially dead for two minutes, which he spent in Hell. Unfortunately for the young Constantine, time moves at an incredibly slow speed in the underworld, compared to Earth. ("Take it from me, two minutes in Hell is a lifetime.")

His "successful" suicide, which is considered a mortal sin in the eyes of God, has condemned him to Hell upon his eventual death. To escape this fate, he has spent the latter part of his life trying to win back God's favor by battling the forces of Hell, though his time on Earth is brief; Constantine has smoked 30 cigarettes a day since he was 15, and is now dying of lung cancer. Because of the number of demons he has slain, Constantine knows that Satan harbors a specific, personal grudge against him, even though he's destined for Hell. Characters repeatedly express the sentiment that he is the only soul that Satan will leave Hell to reap personally. Constantine's time is mostly spent destroying — permanently 'deporting' them back to Hell — demons who break the "rules" of the game.

Investigating the apparent suicide of Isabel (Rachel Weisz), another seer like Constantine, at the instigation of her identical twin Angela, Constantine discovers Mammon's plot. He needs a powerful psychic to possess, and then needs God's help to be released physically, into the earthly plane. Interrogating the half-demon Balthazar by threatening to give him Last Rites before destroying him, Constantine discovers how Mammon plans to get God's help — "the blood of God", found on the Spear of Destiny. By destroying the body of the psychic with the Spear while Mammon is possessing her, he would be free to walk the Earth. However, Angela, ignoring Constantine's instructions, is kidnapped and possessed.

Chasing after Angela, Constantine confronts a room full of half-breed demons guarding Mammon's attempted entry. His apprentice, Chas Kramer (Shia LaBeouf) blesses the water for the fire suppression system in another room, while Constantine, announcing that he will deport all present as violators, lights his cigarette lighter under a sprinkler which releases the blessed water, then shoots all the present, weakened half-breed demons with bullets made from melted-down crosses, destroying them. Chas and Constantine subdue Mammon. Using telekinesis, Archangel Gabriel (Tilda Swinton) kills Chas. Gabriel tells John he killed Chas for interfering in the "birth." Gabriel incapacitates Constantine and begins to summon Mammon using the Spear of Destiny.

Gabriel, angry at how humans can achieve salvation so easily (by simple repentance), wants Hell on Earth because, in his view, humans are truly noble or heroic only when confronting real adversity. By giving them the ultimate adversity, Gabriel thinks that mankind would become worthy of his divine gifts.

The injured Constantine takes his own life a second time in order to win an audience with Satan, whom he informs of Mammon's plot. Satan defeats Gabriel, who apparently has lost divine favor, and returns Mammon to Hell. Satan then asks what Constantine wants as reward for the information and is surprised when Constantine asks for the release of Angela's sister from Hell. Heaven consequently accepts Constantine for his selflessness. As he begins ascending towards the light, he flips off the Devil. Satan, enraged at having lost Constantine's soul, revives him and removes the cancer from his lungs so that he can live on and prove that he truly belongs in Hell. On the way out of the building, Constantine confronts Gabriel who hasn't fallen, but instead is reduced to human, ironically now meriting the same forgiveness and salvation that he earlier decried as undeserved. He urges Constantine to kill him, but instead of shooting him, Constantine just punches him in the face, introducing him to the new sensation of pain.

Constantine's fate now belongs to him, and at the end, he is seen chewing (presumably) nicotine gum, to kick off smoking.

At the end of the film's credits, Constantine visits Chas' grave, saying that he did a good job and leaves his cigarette lighter on top of the grave. When Constantine is about to leave the graveyard, Chas appears as an angel and is dressed as Gabriel was previously. Chas then flies off into the sky. Constantine then smiles to himself.