There has been a major upheaval at Mount Weather. The president has been assassinated. Her running mate, who was her husband, is sworn in as president in order to preserve democracy, but in only a short time his behavior has put the Mount Weather community in a state of turmoil.
If that wasn't bad enough, Chinese soldiers have been discovered on American soil and the zeds, already an ever present danger, are continuing to show signs of cognition and teamwork. The motives of both are unknown but do not bode well for the survivors.