The film powerfully illustrates the corrosive effects of fear - and its close cousin, grief - on its central family. While the audience is given most access to the perspective of the young adult son (a quite good Kelvin Harrison Jr. as Travis), whose nights are constantly disturbed with horrific dream imagery, I think the film is even more interested in his parents. Through Travis, we watch as his parents' fear and overwhelming desire to protect him and each other leads them to the most grim and inexcusable of actions - which, of course, are still not enough to protect the family from the dangers of the world around them. The final shot of Joel Edgerton's Paul and Carmen Ejogo's Sarah staring at each other across a table, alone and infected, is a bleak and emotionally crushing but necessary end to the film because it focuses attention on their actions in the face of the fear of death, and how those actions contrast with Sarah's plea to first her father and then her son to "let go". It's easy to tell someone without hope of survival to let go, that it will be OK... but not as easy to act on that directive when you think you can still make it out alive.

I think the audience expectations for a film with this title dovetail with the way Shults constantly stages scenes to suggest that there's something more horrific and less banal than the plague of death that already surrounds its characters, when in fact there's nothing coming at night except the fear that keeps Travis sleepless and drives his parents' actions. Shults expertly beckons the audience to a place where the expectation of unknown horrors makes them more susceptible to the stark "ends justifying means" mindset that drives Paul and Sarah to do what they do, and makes the lack of reveal of the suggested greater threat harder to process than the more straightforward morality tale Shults is actually telling here. The film accelerates the timeline of Paul and Sarah having to face the ultimate reality of what they've done, but even if they'd survived the plague and society had reconstituted itself, it's easy to imagine the couple eventually having to face mortality again, and sharing the same look that ends the film, questioning the cost of their brief respite from the fear of death.