Sarah is agoraphobic. She refuses to go outside and is paranoid about her daughter Evie going out. She refuses to take her antipsychotics because they make her sleep all the time and she's paranoid that the men who raped her as a teenager (conceiving Evie), will come while she's asleep, like they did when she was young.
As a result, she hallucinates and is delusional.
When Evie starts being influenced by the manic ramblings of the old homeless woman in the street, prophesizing a dark Antichrist to come with the coming solar eclipse, Sarah begins to see a change in her daughter. The girl has been watching the news of the impending eclipse and global hysteria brought about by Doomsday cults and an asteroid that's seemingly on track to hit Earth at the same time as the eclipse.
People are panicking and Evie begins to believe that she must be the Antichrist these cults are talking about. Sarah worries that her daughter has developed a mental illness and contacts her ex psychiatrist, Thomas, to ask him to prescribe her antipsychotics and have them sent. Thomas refuses to, the girl will need to be assessed. He urges Sarah to bring her to a hospital. She hangs up, too paranoid to contemplate such a thought.
Yet when Evie begins to talk about needing to be killed, so that she doesn't become the Antichrist that will inherit the Earth, Sarah decides to leave the house and take her daughter on a road trip to see Thomas and force him to help.
Along the way, they see the world falling apart, chaos and debauchery as they weave through the hysteria.
But Evie's talk begins to infect Sarah, as her own belief of who the men were that raped her and their motivations, begin to intertwine with Evie's belief of why she's here. Although Thomas tries to be the voice of reason, Sarah becomes convinced that her daughter is the Antichrist and must be killed. Evie tells her this must be done.
As the eclipse casts its shadow across the Earth and the fiery ball of asteroid glides closer, Sarah takes her daughter to the beach of her childhood dreams to perform a sacrifice in front of hordes of rioting doomsayers who are fighting among their own bloodbath. Thomas gets there just in time to see the girl ceremoniously killed by her mother. As the light shines back on the Earth and the asteroid passes, calm permeates the crowd.
And as we pull back to see the carnage of mass hysteria, we wonder if Evie was right, or if she was caught in the delusion of her mother's lifelong anguish and global panic that the now shell-shocked Thomas tried to warn them about.