After having been berated by a Judge, Mike Hammer goes for a walk on a rainy night in Manhattan and comes across a terrified woman and her pursuer on a bridge. He kills the man but the woman, terrified, jumps to her death from the bridge. Each possessed an oddly shaped green card, a clue that Hammer pursues. His friend in the police department, Pat Chambers, identifies them as membership cards for the local Communist Party. Mike attends a meeting and is mistaken for a spy from Moscow. At the same time, the FBI is searching for some lost secret papers and the career of a popular politician is threatened.
This novel illustrates the cardinal features of the sub-genre known as hard-boiled crime fiction. The protagonist, Mike Hammer, feels alienated from mainstream society whose values, he feels, are no match for the evil that he must deal with. In the book's opening scene, Hammer walks on a rainy night and reviews the ways in which mainstream society labels him a killer, and he questions whether there is some truth to a judge's denunciation of his actions. He wonders if he is like the evil people he fights.
In hard-boiled crime fiction, commonly the cynical detective narrates in first-person his attempts to deal with a criminal element that the police are ill-equipped to handle, often because the legal system is not up to the task.