Siege

This is humanity's last stand. Threatened on all sides by enemies they can't fight and often can't even comprehend, the human race has taken refuge in an inhospitable corner of the galaxy. A tiny pocket of habitable space concealed by black holes and dust clouds, hiding a cluster of colonies where the last humans in the galaxy reside, preparing themselves for a war of annihilation against all comers. Crystallia is a hidden military base that guards the access route to the colonies. The main mission of the soldiers there is to remain undetected for as long as possible, to spot any incursions from the outside and to hit them with everything in humanity's arsenal. No one is quite convinced that this strategy will be enough to save the colonies or even to create enough of a delay for some of the colonists to escape. The best bet for the human race is to remain concealed. Unfortunately, something has found them.