A peaceful afternoon is shattered when a sniper opens fire on a crowded city plaza. All that remains are three dead victims and mysteriously-numbered shell casings. Convinced the shootings are not random, Chase and August are just beginning their investigation when a major earthquake hits Los Angeles, throwing the city into chaos. Making matters worse, a city-wide Blue Flu forces the detectives to assume beat cop responsibilities. Meanwhile, James leads rescue efforts to find survivors in a badly-damaged apartment complex as aftershocks continue to hit.