User blog comment:Batmannp/Batman: Arkham 4/@comment-4518608-20130922162942

I have my own personnel idea. Prisoners from Arkham Asylum and Blackgate are loose. They've sealed off the city so now help is coming in. They've been in control f the city while Batman was injured during the breakout. The villians have control of Gotham and he, along with Robin, Nightwing and others, has to take them down.

Possible villians: League of Assassin's (they organise it and then swoop in and kill all the villians, making the world agree with their methods), Red Hood (for the same reason and to get back at Batman), Great White Shark and Prometheus.

It's called Arkham Night (because it happens in one night).