Necropolis. City of the Dead - Liberty City island is under quarantine. Any attempt to get off the island will be thwarted. Use the boat or helicopter at your own risk. In addition to the zombie hordes, you also have a few problems. Weapon shops are closed, and most of the weapons, armor and ammunition were taken when the citizens were evacuated. And, I promise you, hot dog vendors don't stick around. You will have to make do with a limited arsenal and fewer options to regenerate health. However, staying in a safehouse will replenish your ammo and some of your health again.
There is a set of elementary missions, collecting, searching and supplying survivors. The living people you save will accompany you as bodyguards, and some of them will even have special abilities to help you (for example, a mechanic will repair your car during your stay at the safe house)