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.

Catherine, Sophia, Zoe and the other survivors, finally reunited, prepare for the ultimate attack. But it is Bill who is the only one to hold the fate of humanity in his hands, provided he is helped by Isla.

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?

At the university, Sophia watches the videos recorded by Dylan, a young man they found dead, while Catherine focuses on the algorithms he left behind and which decipher the behavior of robots. Thanks to Bill's intervention, Isla manages to flee and join her family.

After saving humanity, Bill Ward finds himself locked up in prison. Bitter, he will take a close interest in a new subject: many people around the world are victims of mysterious visions, including MI5 agent Zoe. Meanwhile, the discovery of a black hole prompts Catherine to investigate this global phenomenon.

As Emily grows concerned by her recollections of time spent with the aliens, Bill is also perturbed by the similarities between Emily and the aliens; Zoe encourages a reluctant Bill to use these similarities to their advantage.

Astronauts Juliet Arquette and Richard Gallagher witness Catherine's theories in space as Adina plots revenge against humanity. Mourning over the death of her sister, Catherine decides to research the phenomenon with the help of Johannes. An unexpected encounter prompts Kariem to continue her investigation of global psychosis. Faced with the damage caused by Adina's latest attacks, Zoe decides to turn to Bill to thwart the alien's plans.

Martha unwittingly unleashes a fatal gunfight resulting in severe damage. In the alternate world, Catherine and Sam arrive at their destination, but encounter some unforeseen events. Bill then tries to contact Catherine, but when he can't reach her, he turns to a drastic solution.

Bill investigates more of Catherine's findings and thwarts the aliens' deadly plans, but the group finds themselves in danger once again. Meanwhile, a run-in with the aliens ends tragically. Catherine secretly hatches a plan against her captors, but will she abandon Sam?

Betrayed, Tom forges an unexpected alliance with Zoe. Confronted with the teenager, Bill must again answer for the consequences of his sacrifice. Zoe takes a drastic step to stop Adina's plan. From the alternate world, Catherine discovers that interstellar activity is badly affecting people. She sets out to find a solution, but is in serious danger.

Bill secretly injects Emily with a biological weapon he hopes to use on the aliens; when she becomes sick, some of the survivors head out to find insulin in order to treat her; the resistance base is attacked and the survivors are forced to flee.

Richard discovers new data on the global phenomenon. Catherine must take a risk to continue her research, but is she ready to do it? Meanwhile, a new revelation tests Martha's loyalty, and Zoe is forced to make an urgent sacrifice with the help of her newfound allies.

Catherine shares vital information about the black hole with Richard. Martha discovers Adina's destructive plan which the resistance group confronts. With little time left, the group is forced to take ever greater risks and make painful sacrifices to save the world.

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?