When the novel begins, Spade is having an affair with the wife of his own partner--a very bad choice for such a smart man. If Miles Archer hadn't been shot, he undoubtedly would have found out about Spade and Iva. At the least, that would have destroyed the partnership, but it could have led to Spade being murdered.
Spade accepts a retainer fee from Joel Cairo even though he is already representing Brigid O'Shaughnessy. It is certainly unclear whether Spade intends to give the falcon to Cairo or Brigid, if he ever gets hold of it. Then he makes a deal to give it to Casper Gutman, even though he doesn't have it. In the end he sells it to Gutman for ten thousand dollars, but it is unclear whether he intends to keep the money and let Gutman go, or whether he will report him and Wilmer to the police and relinquish the money.
He is having a love affair with Brigid, but he has been sure all along she was the person who killed Miles Archer in Burritt Street.
"Miles hadn't many brains, but, Christ! he had too many years' experience as a detective to be caught like that by the man he was shadowing. Up a blind alley with his gun tucked away on his hip and his overcoat buttoned? Not a chance.
The reader is never sure what Spade is thinking or what he will do next. Would he have kept the ten thousand dollars if the falcon had been real? If it had been real, why let go of it for only ten thousand dollars when, according to Gutman, it had to be worth many millions?
Spade and Brigid have a significant exchange of dialogue just before the police arrive.
"Look at me," she said, "and tell me the truth. Would you have done this to me if the falcon had been real and you had been paid your money?"
"What difference does that make now? Don't be too sure I'm as crooked as I'm supposed to be. That kind of reputation might be good business--bringing in high-priced jobs and making it easier to deal with the enemy."
Spade doesn't trust anybody because he believes there is wickedness in everybody. He must recognize that wickedness in himself. "He looked rather pleasantly like a blond satan." He is not a knight in armor. His own secretary, who adores him, is horrified by the way he sends Brigid O'Shaughnessy off to San Quentin, where she may be hanged or may get off with a life sentence, of which Spade tells her she would have to serve twenty years on good behavior.
Effie Perrine asks:
"You did that, Sam, to her?"
He nodded. "Your Sam's a detective." . . . He put his arm around her waist, his hand on her hip. "She did kill Miles, angel," he said gently, "offhand, like that."
She escaped from his arm as if it had hurt her. "Don't, please, don't touch me," she said brokenly. "I know--I know you're right. You're right. But don't touch me now--not now."
Spade has plenty of women, apparently including his own secretary, yet he lives alone in one of those San Francisco apartments with a Murphy bed that comes down at night to make a bedroom and goes up by day to make a living-room. He is a lonely man in spite of all his conquests. Dashiell Hammett, who lived in one of those apartments, describes Spade's as follows:
Cold steamy air blew in through two open windows, bringing with it half a dozen times a minute the Alcatraz foghorn's dull moaning. A tinny alarm-clock, insecurely mounted on a corner of Duke's Celebrated Criminal Cases of America--face down on the table--held its hands at five minutes past two.
Spade may live in such a place for the rest of his life.