So far, reading a Richard Stark book is a meditative practice of being with an object that is a form of perfection. Lean, not a word wasted, and right to the point, the main character Parker has a Zen like intensity to his mission in life - robbery.
He also has a distate for those who don't follow the plan which is to rob and then share the loot. "The Sour Lemon Score"" is about a loser who kills numerous people for a small amount of money and you eventually Parker will get back at this double-dealing creep in no time. Because Parker is like a shark. He's totally focused on getting what he agreed to get in the first place. We the readers are interested in seeing the weak criminal get his just awards - but Parker is really only interested in getting what is owed to him - which is a small amount of the money that was robbed in a bank.
Parker is not crazy, nor does he have a great deal of passion, but what he sees himself as is a total professional. He takes pride in his work, yet he doesn't really judge other people. He is only concerned about his actions in the affair. He's loyal to a point that he will do his part in the job, but it is almost indifference when someone in the gang screws up. That is their affair. But for him he agreed to do crime to get a certain X amount of dollars and he won't take less then that. If he agrees to share the loot, that is only what he wants.
Yet the greed of his criminal(s) leads to a major downfall to their world. Yet Parker rises over the damage and sees himself as just a worker getting what he deserves or worked for. "The Sour Lemon Score" is another act of perfection in a world that is not perfect.