After decades of peace, mankind discovers that it is not alone in the universe and is pulled into a war with an unknown alien species. A group of new recruits in the United States Marine Corp are thrown into the heat of battle. They each joined for there own reason, but in the end they are all fighting for the same thing, Earth and the survival of the human race.

A sentry-duty assignment leads the 58th into a confrontation with a battalion of androids, among which are the AIs who murdered Shane's parents.