The colonists of the planet Montana are accustomed to being ignored. Situated in the buffer zone between two rival human empires, their world is a backwater: remote, provincial, independently minded. Even as a provisional member of the Republic of Aligned Worlds, Montana merits little consideration—until it becomes the flashpoint in an impending interstellar war.

When pirate raids threaten to destabilize the region, the RAW deploys its mechanized armored infantry to deal with the situation. Leading the assault is Marine Corps Lieutenant and Montanan expatriate Promise Paen of Victor Company. Years earlier, Promise was driven to join the Marines after her father was killed by such a raid. Payback is sweet, but it comes at a tremendous and devastating cost. And Promise is in no way happy to be back on her birthworld, not even when she is hailed as a hero by the planet's populace, including its colorful president. Making matters even worse: Promise is persistently haunted by the voice of her dead mother.

Meanwhile, the RAW's most bitter rival, the Lusitanian Empire, has been watching events unfold in the Montana system with interest. Their forces have been awaiting the right moment to gain a beachhead in Republic territory, and with Promise's Marines decimated, they believe the time to strike is now.

Unbreakable by W.C. Bauers is character-driven military science fiction featuring a female marine caught between two empires.