There is no abstract Evil; you have to understand that! Its roots are here, all around us, in this herd that goes on chewing and having a good time only an hour after a murder! That's what you have to fight for. For people. Evil is a hydra with many heads, and the more of them you cut off, the more it grows! Hydras have to be starved to death, do you understand that? Kill a hundred Dark Ones, and a thousand more will take their place.
Sergei Lukyanenko, Night Watch
among-his-own-kind, boris-ignatievich-geser, evil