I'm bringing back an old legend.
New story, new plot, new everything and anything.
You are in a mall. Zombies have broken into the mall, with hundreds of civilians at high risk. You hear that they came from a failed test; Zero Ops. You have to get out of the mall, save all the civilians, and go to the Geno-space lab. Find the test rooms and destroy them. Destroy all remaining, unused, bottles of the Zero Ops fluid. If your bitten by a zombie, you have 10 minutes to find an antidote. Luckily, they are easy to find. If you don't, you stay out for 5 rounds.
Like Shadow said,
This is a game when you do an action and the ''game master'' tells you the outcome.