The motif of the knight is present throughout The Big Sleep in that it is a point of comparison with Marlowe that continuously comes into the picture. The book begins with a symbol of the knight in the form of the stained glass (a portrait of a knight rescuing a lady) and continues later on when a chessboard appears (upon which the knight piece is moved). These symbols that contribute to this motif are discussed further in the "Symbols" section below.
The appearances of this motif imply that Marlowe is a knight of sorts. He does not take advantage of Carmen Sternwood, and he seeks out truth even when he is not being paid—as we see in the quest for Rusty Regan, for example. In the end, however, the knight solves the dilemma, but justice is not necessarily served to all. Eddie Mars goes free and the truth is not for all to know; although Marlowe knows the truth, he will not share it with his client. We might fairly ask how knightly Marlowe's behavior is, and whether or not he remains a knight throughout, given that he consistently says that this is not a world in which knights can prevail. In one sense, Marlowe appears to fulfill his duties because he holds the truth from his client for the sole purpose of not wanting to injure him. This, however, has a flip side, as the truth is an ideal, something Marlowe has wanted to reach. The answer to all of these questions lies in the fact that he is a modern day night, perhaps—a knight who, within the realm of reality in 1930s Los Angeles rather than the realm of the stained glass, must bend his morals.
Throughout the novel, weather is always a part of the descriptions of the setting and environment. From the beginning, the sound of thunder rolls forth from the foothills. Significantly, the thunder seems to be coming from where Regan is lying dead. Indeed, the weather mirrors seemingly every chapter and every action. Chandler uses the weather, the rain, and the occasional sun (on a good day, when something is about to unveil itself, for instance, or when the worst seems to be over) as a representative of human emotion.