A sudden rain disrupted everything.
No one knew there was something wrapped in the rain. Invisible eggs seep into the soil with rainwater, flow into pipes, and float into every window that is not closed tightly. A week later, the infected began to appear - first there was something crawling under the skin, like something swimming in the blood vessels; then there was abnormal behavior, with straight eyes and unstoppable saliva; finally there was complete deformation, the skin cracked, and the person became a monster, and the person was no longer human.
Cats, dogs, rats, no one was spared.
The city fell within a month. The survivors are hiding in the ruins and in dark corners. The terrifying monsters do not need light or heat, they only need a host.
And you and me, we just haven't been found yet.