The fourth season tells the story of Captain Tom Chandler (Eric Dane) of the Navy destroyer Nathan James, who puts aside his heroic identity and duties and lives in anonymity with his family in a small fishing village in Greece. At this time, Slattery (Adam Baldwin) and the crew discover that although the virus cannot infect humans, it has mutated into food crops that can infect the world, putting mankind at risk of a global famine crisis.