An espionage or spy mystery is a subgenre of thriller or mystery fiction that revolves around espionage, intelligence agencies, and undercover operations. These stories typically feature spies, secret agents, and government operatives engaged in covert missions, espionage, and counterintelligence activities. Espionage mysteries often involve complex plots, political intrigue, and high-stakes espionage operations, with protagonists navigating a web of deception, betrayal, and danger as they uncover hidden agendas and thwart enemy plots.

Spy thrillers and spy mysteries are often used interchangeably to refer to stories in this genre. However, while both genres focus on espionage and undercover operations, there can be some distinctions between them. Spy thrillers tend to emphasize action, adventure, and high-octane suspense, with fast-paced plots, daring missions, and intense action sequences. In contrast, spy mysteries may place greater emphasis on the mystery aspect, with protagonists unraveling espionage-related puzzles, uncovering hidden conspiracies, and solving mysteries related to espionage activities.