Dead Rising 2: Case West acts as an epilogue to Dead Rising 2. It is available on the Xbox Live marketplace for 800 Microsoft Points ($10). Case Zero takes place in a Phenotrans facility, where Chuch Green and Frank West (Protagonist from Dead Rising) have to unveil the truth behind Phenotrans's mission.
Player be warned: this game can contain spoilers for the retail game. If you haven't played Dead Rising 2 yet, or plan to do so, certain elements may be spoiled.