Lovers Cecily and Frank are infected with a virus when an army truck overturns outside their care home. The virus makes them feel young and strengthened but they pay the price in eating flesh, young flesh. Cecily escapes with a horde of OAPs through the woods as the army hunts them down, but loses Frank on the way.

Kelly, Charlie and Steff find themselves in uncharted territory when they have to dispose of Janine's body. They manage to get away with it, but Kelly is greatly disturbed by her dad's reaction. Charlie tries to comfort her and Steff feels left out, leading him to confide in Finn about the events of the previous day.

Jason is in a critical condition and Kelly's barely hanging on when the army start detaining the infected at their medical centre. Charlie offers a shoulder to cry on but a misjudged comment ends with the two of the fighting. Charlie is shocked but happy to discover his big sister Billy has returned from the army.

Cecily's world is turned upside down when she discovers that Frank has sided with Janine and has eaten his family members. A split breaks across the horde and Cecily is cast out. Finn is starting to feel the effects of the virus and the others decide to take her to Morgan. Finn lets the cat out of the bag about Steff and Kelly's sexual entanglement, which threatens to tear the gang apart.

Having survived the night, Charlie, Kelly, Steff and Finn are taking stock at Steff's house when the horde attacks and splits the gang in two: Charlie and Kelly take a weakening Finn to Morgan's house, whilst Steff diverts the horde away. Morgan hopes to create a cure with the kids' help, but Charlie leaves to find Steff - he can't let his best friend die.

Wrollen enacts the contingency plan and a bomb makes its way to Dambury. With the cure in hand, Kelly, Finn, Cecily and Morgan are trying to make their way out of town but a newly infected Steff blocks their way, forcing Finn to fight him and allowing the others to make an escape.