Though most may require little more than a premise involving zombies, a besieged casino and a chainsaw-wielding motorcycle to get hooked on Dead Rising 2's ultra-violent charms, perhaps you demand greater narrative fortitude from your gaming pleasures. Perhaps you're a thespian, desperately seeking an answer for untold undead anarchy. What is my motivation? you wonder as you route another rigor-mortis special.

Well, you'll have to turn to Dead Rising 2: Case Zero, a "game add-on" launching exclusively on Xbox Live shortly before the full game's release on August 31. Case Zero will serve as a prologue to Dead Rising 2, introducing new protagonist Chuck Greene (who has not covered wars as far as we know) and elaborating on the events that followed the first game.

Pricing and exact release details have yet to be announced. It's also currently unclear how the add-on will work prior to the launch of the full game -- it may be packaged as a separate downloadable game, a la Halo Waypoint, that can interact with Dead Rising 2 ... and explain where all those zombies came from.