It's six months after the initial infection and the U.S. army have restored order and are slowly bringing British citizens back to a quarantined London, where a heavily guarded community is picking up the pieces and trying to return to normal life. Into this precarious situation come Andy and Tammy, a brother and sister who were lucky enough to be on a foreign school trip when the virus originally broke out. Reunited with their father, Don, they learn that their mother perished in the first few days of the outbreak. Desperate to hold on to her memory the two children slip past their guards and make their way back to their old family home where a surprise awaits them; a surprise that threatens to re-ignite the infection all over again.