Jessie is an 11-year-old girl from the rural town of Cedar, Washington. She is friendly, sensitive, and resilient, harboring a deep love for the natural world that she inherited from her late father. She carries the emotional weight of her father's passing and worries about her hardworking mother, but she finds comfort and courage through her tight bond with her best friends.

Eddie is an 11-year-old boy from Cedar who shares matching buzz-cut hair, green eyes, and freckles with his twin brother. Unlike his sibling, Eddie is quiet, serious, and easily spooked by scary stories. Despite his hesitations, he remains fiercely loyal and always supports his friends through their adventures.

Sam is Eddie's 11-year-old twin brother and an avid baseball fan who frequently wears a Seattle Mariners jersey. He has an outgoing, confident personality and a fearless streak that often propels the friend group into new adventures. His risk-taking nature and enthusiasm make him the driving force behind the group's decision to explore the mountain.

Skip is the fun-loving father of Eddie and Sam. He is a robust outdoorsman with a big belly, bushy beard, and a jovial personality that reminds Jessie of a younger version of Santa Claus. He enjoys sharing his love for fishing and the wilderness with his sons and their friends.

Jessie's mother is a hardworking single parent who runs a local diner following the tragic death of her husband. She is a patient and loving parent who provides steady reassurance to her daughter despite her own lingering grief. She harbors quiet dreams of becoming a teacher and starting fresh in a bigger city.

Dr. Morales is a seismologist from the University of Washington who studies Mount St. Helens. With overgrown curls and faded jeans, he looks more like a rock musician than a traditional scientist. He is adventurous, friendly, and dedicated to educating locals about the mountain's imminent danger.

Jessie's late father died in a car accident two years prior to the story's events. He was an avid nature lover who saved up for years to buy a high-quality camera, dreaming of one day having his photography featured in an exhibition. His memory heavily influences his daughter's connection to the outdoors.

Missy is Jessie's former friend and current classmate in Cedar. She shares rumors about a witch living on the mountain and bets the main trio that they are too scared to photograph the abandoned shack.

Gretchen is an older woman who lives in a cabin near Mount St. Helens. She is solitary and deeply respects the forest and its wildlife, preferring to keep loggers away from her home to protect the natural environment.