The novel is basically without plot, instead episodically depicting the psychological changes in three LAPD officers caused by their police work, and particularly the nature of police work in poor minority communities of Los Angeles. The three officer: Serge Duran, Gus Plebesly, and Roy Fehler, are classmates at the police academy in the summer of 1960, and the novel examines their lives each August of succeeding years, culminating in their on-the-job reunion during the Watts riots of August 1965.
The New Centurions is likely the most autobiographical of Wambaugh's novels. He provides a straightforward narration of events with little use of flashback. Each chapter is written in the third-person from the point of view of one of the three protagonists. They have no contact with each other once they graduate from the academy, but their paths are similar and converging. Like Wambaugh, his protagonists move from a few years of uniformed patrol in minority districts to plain clothes assignments in juvenile and vice work, experiences which so affected Wambaugh that he returns to them repeatedly as plot elements in his fiction.
Wambaugh also explores the officers' private lives, noting adultery, alcoholism, racism and suicide as rampant in the ranks of the LAPD. Police suicide, in particular, is a theme Wambaugh explores in nearly all of his books.
A major theme explored throughout the book is what traits characterize a veteran officer, and how a rookie acquires them. Wambaugh consistently compares the attitudes of the new officers (one is not considered a veteran in the LAPD until one's fifth anniversary on the job) to those of the older entrenched men.