Terminal Alliance – Jim C. Hines

“You appear to be trying to shoot an enemy battleship with cans of bleach. Would you like help with that?”

Two centuries earlier, there was a zombie apocalypse. (Surviving humans are not undead, but they are no smarter than zombies and - a never-explained side-effect - no easier to kill.) Now an offworld alliance is trapping feral humans and rehabilitating them. Rehabilitated humans have their intelligence restored (they keep the physical improvements), receive training, and are employed as soldiers. (The term ‘mercenary’ appears, but it’s not a hiring procedure in which the pay is negotiable or refusal to sign up is an option.)

A bio-weapon reverts all the humans on a war ship to feral - except the janitorial crew. When high command is informed it is, surprisingly, more interested in burying the problem than in fixing it. The survivors decide to track down the source of the bio-weapon, rather than to play a starring role in the burial. Space opera ensues.

A fun book to read, humorous (a bit on the slapstick side) and engaging.