With doubt still surrounding the tragedy at the White House, Sterling (Zeljko Ivanek) encounters an unlikely ally in Simon (Ian Anthony Dale), who risks his life to return with a possible antidote. Against the wishes of Chief of Staff Richard Peel (guest star Roger Bart, Desperate Housewives), Jarvis (Bill Smitrovich) authorizes an air strike to neutralize them. Meanwhile, Sophia (Laura Innes) continues on her diabolical plan to exterminate the human race, now with the help of an unwitting accomplice -- Leila (Sarah Roemer). Elsewhere, Sean (Jason Ritter) and Vicky (Taylor Cole) try to prevent the deaths of many thousands of innocent people. Blair Underwood and Lisa Vidal also star.