Burden of Sisyphus (Brink of Distinction book #1‪)‬

Between the alien Alliance and the Terran Empire, a neutral zone stretches between the galaxies, a demilitarized zone that was established 150 years previous, following the Great War. The peace accord granted a semblance of peace to the universe. The peace, however, is a facade, and it is the responsibility of Michael Vance and his covert operations team to maintain that illusion.

Recently, the Alliance lost contact with one of their outposts near the neutral zone. Surveillance scans show an abandoned city and no signs of life. The Alliance does what it always does: send in the best. But an unexpected betrayal leaves Vance and his team stranded. Worse, the city that was supposed to be dead is quite alive. And the monsters that now roam its streets are slaughtering his team, one at a time.