"At heart, most of us are Sam Spade in “The Maltese Falcon,” when he is about to hand over the many-aliased Brigid O’Shaughnessy to the cops for killing his partner, Miles Archer. She asks if Archer meant more to him than she does. She loves him, she says, and he loves her. He says he doesn’t know if that’s so. But he lives by a code. “When a man’s partner is killed,” he says, “he’s supposed to do something about it. It doesn’t make any difference what you thought of him. He was your partner and you’re supposed to do something about it.” When a man’s partner is killed, “it’s bad business to let the killer get away with it. It’s bad all around — bad for that one organization, bad for every detective everywhere.” His struggle is moral. He won’t let her go free “because all of me wants to.” His decision is practical. “And because — God damn you — you’ve counted on that.” The plain truth is that Miss O’Shaughnessy is evil, which makes her his enemy. She asks if he would have acted so high-mindedly if the black bird had proved real and he had been paid his money. He says: “Don’t be too sure I’m as crooked as I’m supposed to be. That sort of reputation might be good business, … making it easier to deal with the enemy."
— The Writer As Detective, Roger Rosenblatt.