A terrorist detonates a dirty bomb in the heart of a densely-populated city, unleashing a gruesome zombie plague that spreads like wildfire. Sarah's father was bleeding out, and she knew he would die if she didn't get him to a hospital fast. The scene that greets them on arrival is one of chaos. The floor, awash with blood, is covered with the bodies of the dying and injured, doctors dart back and forth, clearly overwhelmed. Sarah stumbles back and her world fades to black. Upon regaining consciousness she is greeted by the uneasy silence of a seemingly deserted building....