No one know what went wrong that day. That day was horrible as the whole city was taken over by the zombies. It came like a thief in the night since no one was prepared and most of the people were eaten and got turned into zombies. Fortunately, a doctor has a cure for the disease, but first he would need to escape out of the city and be taken to the government facility.
The doctor has the vaccine and you need to protect him at all cost. Shoot the zombies as they appear and make sure that none of them got close to you. After eliminating the zombies, drive the van to the parking area.