Halfway through sixth grade, Noah's best friend and the only other trans boy in his school, Lewis, passed away in a car accident. Adventurous and curious, Lewis was always bringing a new paranormal story to share with Noah. Together they daydreamed about cryptids and shared discovering their genders and names.

After Lewis's death, lonely and yearning for someone who could understand him like Lewis once did, Noah starts writing letters to Mothman, wondering if he would understand how Noah feels and also looking for evidence of Mothman's existence in the vast woods surrounding his small Poconos town. Noah becomes determined to make his science fair project about Mothman, despite his teachers and parents urging him to make a project about something "real."

Meanwhile, as Noah tries to find Mothman, he also starts to make friends with a group of girls in his grade, Hanna, Molly, and Alice, with whom he'd been friendly, but never close to. Now, they welcome him, and he starts to open up to each of them, especially Hanna, whom Noah has a crush on. But as strange things start to happen and Noah becomes sure of Mothman's existence, his parents and teachers don't believe him. Noah decides it's up to him to risk everything, trek into the woods, and find Mothman himself.