I first read this book a decade or so ago while reading a list of pulp mystery novels, a list that I enjoyed much more than I expected to. McCoy's book stood out because of the extended metaphor and its reference to a historical phenomenon I had not been familiar with. Less a mystery than just plain pulp, the book tells the story of a couple who go to make some money, to survive, during the Great Depression, by joining a dance marathon.
Dance marathons were popular for some time during the 1930s. Essentially contests in which couples danced for as long as possible, until they were the last couple standing, they were entertainment spectacles. Here, however, the marathon is a metaphor for life--a tough and grueling life. The couple can't leave the floor; it has to remain to eat (food is provided) and to have a chance at the thousand-dollar prize that will give them a new start in life, if they want it, that is, for the woman, Gloria, has already given up on life: she just wants to die, if only she had the guts to do herself in.
And that is the gist of the book, how her dance partner is finally convinced to kill the woman as a favor to her, as the dance marathon moves forward despite petty crime, crooks hanging out in disguise, affairs, better morals society protests, and so on.