An experiment conducted in a high-security laboratory aimed to develop a parasite capable of repairing tissues and accelerating regeneration. During the last trials, an unexpected mutation occurred. The parasite has begun to take control of its hosts' brains, gradually erasing their personality to leave only an instinct for propagation. The lockdown failed. In a few days, the researchers were the first to fall, followed by the soldiers responsible for securing the premises. Major cities followed. Governments have collapsed and the few survivors now live in hiding, constantly threatened by the infected.