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.