Capt. Tom Chandler and his crew set out for the Arctic with two virologists; Chandler discovers that the virologists are collecting samples of the source of a virus that has wiped out more than half of the human population while he has been at sea.
After the horrifying revelations and reversals of fortune in Baltimore, Chandler and his fractured team join forces with an underground resistance in an attempt to defeat Amy Granderson.
Nathan James returns home to Norfolk on a mission to produce and distribute the cure; Chandler sends his crew in search of their own friends and loved ones.
Chandler and his crew head to the U.S. military base in Guantanamo Bay in search of food, medical supplies and fuel; escaped prisoners attack the search teams; the teams enlist the help of a private contractor.
A small team heads to the jungles of Nicaragua to find monkeys for Rachel's vaccine trials; Chandler and his men face a moral dilemma when they encounter a former drug kingpin.