First published in the US in 1961, ''The Ace of Spades'' is a classic police procedural, the second installment in the long-running Lieutenant Luis Mendoza mystery series, which eventually spanned 36 novels. The author was a pioneer in the male-dominated crime fiction genre, widely celebrated as the "Queen of the Procedurals" for her realistic, multi-layered portrayals of police work.

The story follows Lieutenant Luis Mendoza, the wealthy, sharp-witted, and debonair head of the LAPD's Homicide unit who has a distinct fondness for poker, fine tailoring, and Abyssinian cats. The plot kicks off through an unusual connection to Mendoza's personal life when his girlfriend, Alison Weir, has her old, beat-up jalopy stolen. When the car is recovered, Alison discovers a rare, antique coin-like object slipped deep into the seat cushions. Meanwhile, Mendoza is investigating a seemingly unrelated homicide where the only clue is a cryptic scrap of paper found in a dead man's pocket bearing the words "nymph" and "small dolphin".

As the LAPD digs deeper, these minor details untangle a sprawling web of criminal activity involving:
An apparent drug-induced suicide
A high-stakes museum coin heist
A ring of illicit importers and a mysterious figure known as Madam K

The investigation intensifies into a race against time when Mendoza realizes the criminals know where the missing coin went, putting Alison's life in immediate danger.