Jerald Walker has five years of experience at Black Mesa when an SOS signal arrives from a base that has been established in Xena. He responds. Upon arrival, he finds survivors who share critical intelligence, and he also discovers a new experimental sample: a purple crystal. The trouble that follows comes in layers — a failed experiment triggers a cascade resonance, and while alien forces are already attacking, a mercenary unit from the Black Hawk organization descends on the base as a second simultaneous threat. Jerald works through all of it with improvised firepower, and the further he goes, the more of the larger picture comes into focus.