Mistress Mayhem by Miranda May

Mayhem.
Violent or damaging disorder; chaos.
It is what our world fell into hundreds of years ago. Murder on the street. Parents abusing their children. Rape. Drugs. Guns. The streets ran red.
It all culminated into the Last War—the war that almost ended the human species. Bombs. Killings. Cyber attacks. You name it, they tried it.
Once the smoke lifted, less than a quarter of the population had survived. They knew that the only way that they would survive would be peace. Not just between countries, but between one another. Crime could no longer happen, but telling a killer not to kill, a torturer not to torture? It just makes them want to do it more.
So it was decided. One night of the year, from dusk until dawn, nothing is illegal. And what better night than Halloween? All Hallows Eve? Samhain? Our Mayhem.
It has worked for us for hundreds of years, but because we are only human—some people just cannot accept that what they have is enough. So they break our laws.
Not to worry because I’m keeping tabs and come Mayhem, they’ll be meeting Mayhem’s Mistress.