When astrophysicists detect a transmission from another galaxy, it is definitive proof of intelligent extra-terrestrial life. The world's population waits for further contact with baited breath. They do not have to wait long. Within days, mankind is all but wiped out; just pockets of humanity are left in an eerily deserted world.

After the devastating alien attack, disparate pockets of survivors emerge into a shattered world. They quickly realise they must put their differences aside if they are to stand any chance of survival. For they are not alone. Something sinister lurks in the shadows and whatever it is, it won't consider its victory complete until it hashuged every last human. But who are these attackers and why are they hell-bent on destruction?

As the dust settles on their brave new world, the survivors are forced to face some cold truths. Catherine is stunned to discover the part she played in bringing about the alien attack. Helen becomes fixated on revenge. And Emily momentarily regains her sight. But is the miracle cause for celebration, or concern?

The survivors make some disarming discoveries not only about the aliens but also about themselves. Mokrani goes on the offensive, taking the fight to the aliens. Ash is forced to make the hardest decision of his life. And Chloe's past catches up with her, threatening to rip apart the delicate semblance of normality she is so desperately clinging on to.

Cracks start to show as the survivors find different ways to cope. Jonathan's increasingly perturbed by Sacha's strange behaviour. Emily proves to be an exciting conundrum for Bill. And Mokrani is horrified as his men delight in the opportunity to exact revenge.

The alien's connection to certain survivors raises difficult questions. Bill makes a startling discovery. Sacha's behaviour is increasingly erratic. And Tom's birthday proves cause for celebration. But at what cost?

Tragedy strikes, altering the course of the future forever. Catherine's priorities change with the arrival of Sophia. Things come to a head between Jonathan and Sacha. And Emily's so happy she can see again that she's stopped asking why, even if others haven't...

Mokrani and Catherine are preparing to fight their lives. Emily, meanwhile, is looking for answers to her many questions, even if she knows that the consequences of the truth could come to light. In addition, Sacha's visions continue, projecting a confusing image of the future...