When a devastating flu-like virus wipes out most of the world's population, a handful of survivors are left struggling to stay alive as society falls apart around them. Abby Grant, a housewife and mother, is among those who remain, and sets out to find her 11-year-old son. Along the way she meets a variety of people spared by fate, and they must stick together if they are to survive this dangerous new world.

Abby and her new friends discover that supplies will not be shared equally in the new world, as they come face to face with a gang of armed thugs who have laid claim to the supermarkets in the area, leaving them short of food and water. Greg, meanwhile, meets a young woman with a tempting proposition for him, which would leave him with a comfortable new life, but would also mean turning his back on the others.

Abby stumbles across a community that could hold the key to everyone's future. The last surviving member of the government, Samantha Willis, has established a community which still has light, food, hot water and power, but to what lengths will she go in order to maintain control? Greg and Tom encounter a family who have successfully sheltered from the virus but when the daughter reaches out to them they face a terrible dilemma.

When Abby learns of a group of young boys living in a nearby mansion, she leaves her new friends in the hope of finding her son. Arriving at the mansion, she finds herself in the middle of a land dispute, and must broker a truce if she is to find Peter. Meanwhile, Tom, Sarah, Al and Najid are drawn to the comfort and security of Samantha's community, and Greg and Anya encounter some unwelcome visitors.

Suspicions are aroused when visionary spiritual leader John turns up mysteriously at the survivors' door with his ragged group of passionate disciples. Is he as innocent as he seems, or does he have more sinister intentions? When Abby allows a pregnant woman from John's group to stay with them until the baby is born, Anya fears that she will be forced to reveal that she is a doctor. John makes Anya fear for the group's safety.

The post-apocalyptic drama series concludes with Abby and her friends on the run from Samantha, who has formed a dangerous alliance that threatens everyone's freedom. Sarah, meanwhile, is confronted by a face from the past, which leads her to betray her new friends, and when Naj goes missing, the family face the danger of the city in order to find him. Time is running out, and Dexter is only a step behind them all.