Next of Kin (novel)

Next of Kin, also known as The Space Willies, is a science fiction comic novel by English writer Eric Frank Russell.

John Leeming is every sergeant's worst nightmare — immune to discipline and punishment, and given to random acts of defiance, such as wearing his cap backwards on parade for no particular reason.

For a while the mission goes well, but eventually some of the ship's "propulsors" fail after long use, and Leeming is forced to land on a world far inside enemy territory, which turns out to be inhabited by a dour, reptilian race who make ideal prison guards.

Furthermore, Leeming alleges that the Lathians, the leaders of the enemy alliance, have invisible companions called Willies, although these are far inferior to Eustaces.

Leeming's captors are convinced by the responses and fear that if they accept more human prisoners, they will have thousands of invisible Eustaces running wild across their planet and causing mayhem.