Two civilian virologists, Drs. Rachel Scott and Quincy Tophet, claiming to be studying birds, join Captain Tom Chandler and crew aboard the USS Nathan James on their way to the Arctic. Renegade Russian forces attack them, and Chandler learns the virologists are actually collecting samples of a deadly virus that has wiped out over half the human population while they have been at sea. The remaining U.S. government orders the ship home, but those aboard realize home is not as they left it. The safest place to develop a vaccine is on their ship in open water.