For Cade Grayson - husband, father, and former Delta Force soldier - that warm, sunny day in July was supposed to be just another ordinary day. His wife and daughter had flown to South Carolina to visit the grandparents, and the house was his. If he quickly tackled his wife's to-do list, he could lounge in his favorite chair for the rest of the day and watch baseball on TV. However, the day would go down in history as Z-Day. In Portland, a protest rally spirals out of control. Hundreds of demonstrators engage in violent clashes with the National Guard. Some eyewitnesses report particularly gruesome, sometimes cannibalistic scenes. As the first victims are admitted to nearby hospitals, it quickly becomes clear that they are dealing with an unknown type of plague.