In 2019, a plague has transformed most of the world's population into vampires. The human population has plummeted and the need for blood becomes desperate. Vampires deprived of blood for long durations degenerate into "subsiders," psychotic bat-like creatures with no memories of who they were and whose only thought is the craving for blood. The few remaining humans are captured and harvested in laboratory farms while scientists research a synthetic Blood substitutes.