Without telling Emily or her parents anything, Bill decides with Zoe to test on Emily the biological weapon he hopes to be able to use against the aliens. Catherine, for her part, has had difficulty managing her grief since Mokrani's death. She now has only one thing on her mind: to find out who Bill Ward is and find him. Sophia is ready to help him, but Nathan hesitates.
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?