After a tragic accident, six friends reunite for a caving expedition. Their adventure soon goes horribly wrong when a collapse traps them deep underground and they find themselves pursued by bloodthirsty creatures. As their friendships deteriorate, they find themselves in a desperate struggle to survive the creatures and each other.

Twenty-eight days after a killer virus was accidentally unleashed from a British research facility, a small group of London survivors are caught in a desperate struggle to protect themselves from the infected. Carried by animals and humans, the virus turns those it infects into homicidal maniacs -- and it's absolutely impossible to contain.