A man wearing a hazmat suit walks into a police station in Siberia claiming he is responsible for the deaths of his wife and three children. Before he can be questioned, he is kidnapped by Gai Dong Jing, his former employer and an ex-Alliance officer who is now head of a secret terrorist cell conducting bioweapon research of deadly proportions. Agents Sydney Bristow and Michael Vaughn are sent to a small town on the Siberian-Korean border to look for Jing's lab. They discover an underground bunker, the place where the mysterious man in the hazmat suit-a brilliant Alliance geneticist who disappeared years ago-was quarantined. With the threat of a worldwide epidemic looming, Sydney and the APO team must locate Jing and decode the scientist's medical diary, which holds the answers to the virus and the fate of his family. In the meantime, the highly contagious geneticist plans to rid himself of his illness in the most unimaginable way. . . .