I’m not doing a Zombies game. I am just using the Zombies 3 expansion pack to build a mall.
My plan was that somebody was doing foul rituals to open a gateway to Infernia in an abandoned fast food place. With the economy the way it is (the game is set in 2008) there are plenty of abandoned shops, and a homeless ex-executive has secretly been doing foul rituals in one of them.
Idea: his rituals summon monsters that chase the patrons out of the mall, including the PCs. Not everybody excapes, and the PCs have to return to try to rescue those who didn’t get out (once they fight their way out the first time).
Basically it becomes like a Mall Dungeon then.