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.

Tom and Greg are enslaved alongside dozens of others in Mr Smithson's coal mine. Elsewhere, the Family are desperately tracking Billy, their only lead, across the country. At a roadside motel Billy stops to meet his girlfriend Sally and when the Family confront him, Billy claims ignorance and exits.

Meanwhile in the mine, Greg formulates an escape plan, convincing Smithson that he's a geologist and has discovered a gas leak. However the Family are converging on Smithson's as well with their own rescue plans, leading to a dangerous game of cat and mouse...

Reunited and on the road, the Family travel south on the look out for a new home. They encounter a small but thriving community of survivors and decide to take up their offer of hospitality.

While Al and Sarah enjoy their new romance, Tom simmers as Anya makes friends with Judy, the community's leader.

Greg and Abby return to Greg's house one last time where Greg spots the mysterious postcard, leading him to an abandoned airfield and an encounter with the disturbed Mr. Stevens.

Meanwhile, Sarah discovers an elderly couple dying from a new, mutant strain of the virus.

The post-apocalyptic drama reaches its thrilling conclusion as the fates of the Family, the Lab and the rest of the world come crashing together in a deadly showdown.