The Blood Service

Aaron's no soldier. He's just a convict—a Capital criminal.They gave him a lifetime sentence at thirteen years old, so that he could toil his remaining days in the Empire's distant galactic colonies. But not every planet the Empire has colonized is empty.
Aaron doesn't need cybernetics to hear the big beasts battering away at the colony wall. These creatures dig day and night, two tons of leather and bone sending violent tremors through the dry soil. They're coming, they're coordinated, vicious and relentless.
Even all of the technology, weapons, and cybernetic soldiers can't beat politics. Orders come down for the garrison to depart, leaving fifty thousand colonists to the whims of their vengeful alien host. There's not enough men to defend their borders...
They may not be soldiers, but the Capital convicts are strong, united, and just desperate enough. The Imperials offer Aaron and his friends a devil's bargain:
Serve a tour, go free.GOODREADS REVIEWS
“The main character is awesome, and the story is action packed!” Goodreads, ★★★★★ “Loved it. Fast-paced and feel-good storyline.” Goodreads, ★★★★★ “This beautifully haunting and poignant adventure…” Goodreads, ★★★★★ “The start of a brilliant series!” Goodreads, ★★★★★SERIES CONTENT:
Would be rated R: contains graphic depictions of war and sci-fi violence, foul language. Sexual activity is acknowledged or faded to black, but with no explicit content.