The Fifth Horseman follows an FBI agent drawn into a deadly pursuit after his partner is killed by a mysterious and highly skilled operative—one who claims to have come from a climate-ravaged future. As the investigation unfolds, the agent discovers a chilling plan to unleash a catastrophic bio-weapon designed to save the planet by eradicating most of humanity. As the clock ticks down, he must stop a man who believes he is not a villain, but the last hope for Earth’s survival.