Orion, portrayed by Jacob Tremblay, is a deeply anxious 11-year-old schoolboy, grappling with an overwhelming array of irrational fears. His worries range from the mundane, like clogging the toilet and somehow flooding his school, to the more intense, such as mosquito bites that could lead to infection or being punched by school bully Richie Panichi (Jack Fisher). Each fear is meticulously documented in his diary, alongside more ludicrous concerns like murderous clowns, dogs, and oceans. As he struggles with his feelings, he becomes increasingly anxious about an upcoming field trip to the planetarium where he hopes to speak to his crush, Sally (Shino Nakamichi), but fear of rejection holds him back.
Despite his parents, Carla Gugino and Matt Dellapina, encouraging him to confront his fears, Orion's nerves lead him to falsely inform his teacher that he hasn't received permission to participate in the outing. His anxiety culminates on a night of unexpected blackouts, where he is visited by Dark, the embodiment of his fears, played by Paul Walter Hauser. Dark, tired of Orion's constant whining, proposes a journey to assist him in overcoming his reluctance toward nighttime and all it entails.
In an attempt to show Orion the more magical elements of the night, Dark introduces him to other night-themed entities, such as Natasia Demetriou as Sleep, Nat Faxon as Insomnia, Aparna Nancherla as Quiet, Golda Rosheuvel as Unexplained Noises, and Angela Bassett as Sweet Dreams. While Dark argues that their cooperation on this journey could be beneficial, the night entities are initially reluctant.
Throughout their adventure, Orion learns about their various roles: Quiet diminishes external sounds, Sleep helps induce slumber using unconventional methods, while Insomnia stirs up anxiety. Gradually, Orion becomes more at ease with Dark and begins aiding them in their nightly duties. However, the arrival of Light (Ike Barinholtz), who represents daytime, complicates their journey. Orion's inadvertent praise for Light, as one who brings comfort and safety, drives a wedge between him and the night entities, who then reconsider their place in the world.
Their troubles come to a peak when Dark, feeling abandoned, stands atop a mountain, leading to a fractious moment for Orion—who guilt-ridden realizes his mistake. The story morphs as we see an adult Orion (Colin Hanks) narrating his childhood adventures to his daughter, Hypatia (Mia Akemi Brown), illustrating how these events shaped his life. Hypatia’s reaction to the tale is one of surprise, prompting her to suggest a different ending, where she resolves to help him through his fears.
As they navigate this new rendition, Orion now finds himself back at a beach where he encounters young Hypatia, who inspires him with a poem. The night entities return, realizing their vital role when the world falters without the balance of night and day. They remember how vital it is for Orion to dream about Dark, which leads them to work together to summon him back to restore harmony.
Ultimately, Orion faces his fears by leaping into the black hole that threatens to consume Dark, allowing them both to escape the dream, just as Quiet wakes Orion up. Dark’s re-emergence brings back the night, revitalizing the world, while Hypatia, bizarrely trapped in the past, awaits transportation back to her time, which arrives via a young boy named Tycho (Nick Kishiyama) from the future.
The tale culminates with an adult Hypatia (Shannon Chan-Kent) recounting her own version of events to her son, Tycho. As the narrative closes, it reconnects with the earlier moments of young Orion and Sally gazing at the stars on their planetarium trip, bringing the story full circle in its exploration of fear, friendship, and the necessity of balance in life.
