This story, first published in 1958, is by one of the old masters of SF. It is set in the far future during an extended war between the human and Sirian space empires. The humans have the edge in technology but the Sirians have far greater numbers, so a novel way must be found to reduce the numbers the Sirians can deploy.
The answer is to send in a "wasp"; the analogy being with a multiple-fatality auto accident caused when a wasp got into the car and started buzzing around the driver. Men with pre-war experience of living on Sirian planets are recruited to be disguised as Sirians (not difficult: they are basically purple-skinned humans) and dropped on Sirian planets to cause as much trouble as possible.
The story follows one wasp – James Mowry – who is deposited with a cache of sabotage/subversion material on one of the target planets. He starts out by creating an imaginary Sirian resistance movement and liberally distributing posters, allegedly from this movement, around towns and cities. He then engineers a number of incidents, which he publicises as the work of his resistance movement, in his efforts to get the Sirian authorities worried enough to divert considerable resources to deal with this threat.
Naturally all does not go to plan, and what follows is a gripping thriller. By modern standards it is very short (140 pages) and the relentless pace meant that I finished it at one sitting.
It is probably thirty years or more since I last read it, and I was curious to see how it stood up. I enjoyed the read but I have to admit that, surprisingly for the author and period, the SF elements are weak. The Sirian planet is virtually the same as Earth; the Sirians are the same as humans in their culture and personalities, and their towns and infrastructure are basically mid-twentieth century Earth, except for electric vehicles running on broadcast power. With a few changes the story could easily have been set on Earth, for instance in Japan in the Second World War; a notion reinforced by a suspicious resemblance between the name of the Sirian secret police – the Kaitempi – and that of the Japanese military police, the Kempetai.
Still, it's an entertaining read and worth the brief time required, should you come across it.