The film is based on DC Comics' "Hellblazer" comic book, with plot elements taken from the "Dangerous Habits" story arc (issues #4146) and the "Original Sins" story arc. The film portrays John Constantine as a cynic with the ability to perceive and communicate with half-angels and half-demons in their true form. He seeks salvation from eternal damnation in Hell for a suicide attempt in his youth. Constantine exorcises demons back to Hell to earn favor with Heaven but has become weary over time. With terminal lung cancer, he helps a troubled police detective learn the truth about her twin sister's death while simultaneously unraveling a much larger and darker plot.