The Concrete Blonde is a "perfect crime" story. As such it is comparable to Williams's A Touch of Evil and The Hot Spot, and to James M. Cain's Double Indemnity and many others. In this kind of story, it goes without saying the perfect crime will not go as planned, and it is excruciating to watch it unravel.
Predictable though the direction of the story may be, endless variations are possible with the motive behind the crime. A thief may want to make one, last, big score and retire. Lovers may want to run away together and be happy. A drifter on the run may want to escape for good. People who have been wronged may want revenge.
Likewise the relationships of the characters are variable. They may be in love or they may may be forced to work together though they hate each other.
In The Concrete Flamingo, Charles Williams comes up with a combination of motive and relationship I haven't seen anywhere else, and this gives the ending its own peculiar flavor. This is my sixth novel by Williams, and so far what Bill Crider said about him proves true: "Anything by Williams is good."