Astronomers discover shocking signals from outer space, and within days, the human race is wiped out, with only a small number of survivors. Then spaceships appear in the sky trying to attack them, and the survivors try to defend themselves against the attackers.
In the second season, Bill learns more about aliens and how much they resemble humans, with Emily being the most like an alien. Catherine and Sophia also have to cope with new personal issues in addition to the alien threat.
Professor Bill Ward succeeds in preserving humanity at the end of the second season, but he suffers from loneliness and decides to stay away from the disturbing news, but the emergence of a new danger to humanity forces him to work with the others to stop a new global catastrophe.