Emily agrees to help Bill test her for the virus, but soon experiences serious side effects. Sacha, who has secretly followed the group to stay close to Emily, tries to remove her from the group. For their part, Catherine, Sophia and Nathan set out again in search of Bill Ward.
When astronomers detect a transmission from another galaxy, it is definitive proof of intelligent extra-terrestrial life. Earth's population waits for further contact with bated breath, but does not have to wait long. Within days, mankind is all but wiped out, with just pockets of humanity are left in an eerily deserted world. As alien ships appear in the sky, the survivors ask a burning question - who are these attackers and why are they hell-bent on our destruction?