Welcome young traveler, the world is in great danger! I need your help to save what is left of it. The Z-Virus is spreading constantly and if we can't find a cure fast, the world as we know it is doomed. I am very close to finding the antidote, all I need is some more time. This is where you come into play. Prevent the Zombies from infiltrating my laboratory. Buy weapons and upgrades and hold them off as long as you can. Godspeed my friend!"
Kill all the zombies, defend the professor, buy weapons and upgrades and hold the doors as long as possible. Will the professor have enough time to find the cure? It's up to you!