Haven’t read it, but it’s about an apocalyptic scenario where normal people turn into absolute psychopaths. The Asian movie The Sadness has a similar premise.

There are different story lines, but the world is one where there is an infection that basically damages the parts of people’s brains that are responsible for morality. They can think and talk, but there is zero impulse control. Lots of rape and murder. It’s pretty fucked. I didn’t read all of what’s out there but what I did read was bleak at best.

It usually follows a small group of survivors a la walking dead.