Carmen's Childlike Behavior (Situational Irony)
From the start, Carmen Sternwood is presented as a kind of childlike presence, giggling, flirting with men by calling them "cute," and biting her thumb like a toddler. While her developmentally arrested behavior can easily be read as pathological from the start, it contrasts with just how dangerous and wicked she proves herself to be. While her emotions are childlike and reckless, when we see the extent to which she follows her sexuality into dangerous situations, and learn that it was she who killed Sean Regan, we realize that her facade of innocence is hiding a profoundly adult darkness. Her innocent baby doll act is a front for her unsettlingly adult attitudes—as represented by her aggressive sexuality and her capacity for violence.
The Corruption of the Police (Situational Irony)
After Marlowe solves the Geiger case, Vivian inexplicably urges him to drop their case and move on to something else, but Marlowe is dissatisfied, all the more encouraged by Vivian's anxiety to investigate the disappearance of Sean Regan. He then gets a call from his friend Bernie at the D.A. office, who tells him that the D.A. office also wants him to stay out of the Sean Regan case. This irony lies in the fact that while the D.A. office ought to want to investigate corruption and a notable disappearance, they are being bribed by Eddie Mars, a gangster. The police themselves have been corrupted and pulled into the world of crime controlled by Eddie Mars. It takes Philip Marlowe, an independent agent, to figure out the case and bring the villains to justice, with no real help from the police.
Mars is Killed By His Own Men (Situational and Dramatic Irony)
When Marlowe apprehends Eddie Mars at Geiger's house, he gets the upper hand and holds him at gunpoint. While the viewer expects the final outcome of the scene to be Marlowe shooting Mars and saving the day, he is able to keep his hands clean and walk away without having killed anyone. Ingeniously, he shoots Mars in the arm, which only wounds him, before pushing Mars out the front door and into his own ambush. Mars is shot dead by his own men, in an ambush planned for the purpose of killing Marlowe. Mars ends up getting accidentally killed by his own men—which is also a form of dramatic irony—and Marlowe is able to walk away from the bloodbath guilt-free.
The Loose Ends of the Plot (Situational Irony)
While making the film, legend has it that Humphrey Bogart came into filming one day and asked director Howard Hawks how the chauffeur Owen Taylor died. Hawks didn't know, so asked the screenwriters, who also said that they didn't know. In a last attempt to clear up the mystery, Hawks called Raymond Chandler, the author of the book on which the film was based; surely the author would have an answer. He did not.
While the plot of the film is complex, jam-packed, and full of twists and turns, it often does not make that much sense. A mystery thriller is often lauded for its deft utilization of plot devices and satisfying narrative turns, but The Big Sleep proves that a thriller can be successful even if those devices leave a trail of loose ends. The film remains satisfying, even if it cannot always deliver clarity or even plausibility.
