What The Big Sleep tells its readers about detective Philip Marlowe is that he is an honest detective in a corrupt world. He is full of integrity and honesty, a man who is willing to seek truth and work for a mere twenty-five dollars a day. In many ways he is even chaste. The best way to understand him is to think of him as many critics have—as a modern-day knight.
Marlowe, in his work, witnesses death, murder, smut, and crime every day—they are a part of his everyday existence—and yet, we come to the realization that Marlowe remains the only honorable character in his everyday world. The novel book opens with Marlowe starring at a piece of stained glass in the Sternwood mansion. The stained glass depicts a knight trying to release a "damsel in distress" from the tree to which she is tied. The woman is described in Marlowe's usual sardonic tone as being naked but having "some very long convenient hair." Perhaps the most significant aspect of this passage is Marlowe's observation that the knight is not getting very far in the feat placed before him. This image of futility causes Marlowe to think to himself that, if he lived in the Sternwood house, he would, sooner or later, have to climb up into the stained glass and help the knight, as the knight does not seem to really be trying. Marlowe's thoughts are important for two reasons. First, they foreshadow the scenes in which Marlowe "rescues" the naked Carmen; second, they make us realize that Marlowe will commit himself completely to the tasks placed before him. He does his task not for the meager pay, but because it is what he feels he must do.
Significantly, Marlowe lives rather poorly, paid only twenty-five dollars a day plus expenses. Nonetheless, he seems inherently driven towards the discovery of truth. Also significant is the fact that Marlowe works towards this truth independently—he does not work directly for the law, but for himself. He is not a "cop," but rather a private detective.
Despite the tough front Marlowe puts up, on the inside he is good and almost sensitive. We see this clearly in the fact that he tells Carmen his name is Doghouse Reilly, even though his real name is Philip Marlowe. Doghouse Reilly seems like a street name, ringing with the same tough-sounding bell that names like Eddie Mars or Canino do, for instance. Regardless, Marlowe's true name is Marlowe—a name that not only sounds knightly, but that, as Peter J. Rabinowitz claims in his essay "Rats behind the Wainscoting: Politics, Convention, and Chandler's The Big Sleep," is also the name of Conrad's protagonist in the classic novel Heart of Darkness. This connection forms an important parallel between the two novels: both characters are idealists in search of truth in a primarily dark world.
By the end of the novel, we must bring Marlowe's knighthood to question and ask ourselves how successful he is as a knight, as a private detective, and as an honorable person. given what he has had to give up and give into throughout his search for truth.
Eddie Mars is a racketeer, a gambler, a "bad guy," and, most importantly, Marlowe's foil. Mars personifies everything Marlowe stands against: he is dirty and crooked, and he is directly or indirectly behind almost every murder in the novel. He is perhaps best described through a passage from the novel itself: "You think he's just a gambler. I think he's a pornographer, a blackmailer, a hot car broker, a killer by remote control, and a suborner of crooked cops. He's whatever looks good to him he never killed anybody, he just hires it done." This is Marlowe's description of Mars to Mona Mars, Mars's wife. Whereas Marlowe does not want to kill anybody and does not often carry a gun, Mars has no qualms about murder—but he always asks someone else to do the actual killing in order to keep the blood off of his own hands.
It is significant that Mars is named after the Roman god of war. His name, then, like Marlowe's, also carries a certain amount of symbolism. Drawing a parallel between The Big Sleep and medieval fairytales of knights, Marlowe stands as the knight and Mars stands as the dragon or evildoer. Going further with this analogy, it might be argued that if Mars is not Marlowe's double or foil, perhaps Mars is Sternwood's double. In this sense, Marlowe is Sternwood's knight, while Canino, Mars's gunman, is Mars's own perverse version of a knight, the degraded knight or fallen angel.
Like Marlowe, Carmen is not what she appears. She appears to be, as her father says a young, childish girl who "likes to pull the wings off flies." Her "flies," however turn out to be much larger than her father imagined. Carmen murders Rusty Regan, the character Marlowe has been searching for futilely. Carmen is so important because she illustrates an inherent "doubleness" that exists throughout the novel.
In a feminist reading, we might see Carmen as a character that is portrayed in a typically anti-feminist manner. She is unintelligent and emotional. She is spoiled just like her sister, Vivian. Carmen is a flirtatious, giggly, beautiful girl with the heart of a murderess. More important, she is mentally instable—a Siren of sorts, much like the deadly Sirens who tempt Odysseus in Homer's Odyssey. The portrayal of women in The Big Sleep is one that can be explored further in the characters of Vivian Sternwood and the attractive Mona Mars.