In the final episode of the series Abby and her friends find themselves on the run from Samantha, who has formed a dangerous alliance that threatens everyone's freedom. Meanwhile, Sarah is confronted by a face from the past, which leads her to betray her new friends.

When Naj goes missing, the family face the danger of the city in order to find him. Naj is befriended by a feral boy named Darren. Darren lives with the sinister Craig and June, who look after a group of children who forage amidst the ruins of the city in return for the shelter and protection.

With his adopted family searching for him in the deserted city, time is rapidly running out, and Dexter is only a step behind them all...

Greg has been wounded by a gunshot, Anya, Al and Tom frantically search a nearby hospital to find vital medical supplies. With the building on fire, it suddenly collapses, leaving Anya and All trapped. Whilst Greg is now perilously close to death.

Abby still remains kidnapped at the Lab as the Scientists seek to find a vaccine using her immune system.

The family, scavenging for survival in the city, discover that other people have been abducted in the same way as Abby. Tom, Al, Anya and Sarah set off in pursuit of a pharmaceutical company with offices in the city, while Greg and Naj are confronted by a group from which Tom has stolen supplies. At the lab, Whittaker re-infects Abby with the virus.