Simon is a seventh-grader with PTSD who survived a mass shooting in his hometown of Eagle Crest. He appreciates the absolute quiet of his new off-grid town, where no one knows his face or history. He uses sarcasm and dark humor as defense mechanisms when interacting with others. He fears unwanted attention and pity but slowly opens up to the possibility of building genuine friendships.

Simon's mother works as a funeral director with an appropriately dark sense of humor, while his father serves as a deacon at the local Catholic church. Both parents are fiercely protective and deal with their own trauma following the violence at Simon's old school. The couple tries to balance giving Simon space to grow with their intense instinct to keep him perfectly safe.

Agate is a highly intelligent, autistic girl with bright orange hair who fully embraces her differences. She lives on a busy farm where her family breeds service dogs and raises Angora goats. Deeply interested in astronomy and sidereal time, she spearheads a secret project to fake a radio signal from space to renew scientists' optimism in the local SETI program.

Kevin is a laid-back seventh-grader with green hair who serves as an altar boy at the local church. He belongs to the scientific community of Grin and Bear It, participating in science fairs and conducting experiments with microwaves. His trusting nature helps Simon feel comfortable, even as Kevin struggles to understand Simon's initial secrecy about his past.

Hercules is the runt of a golden retriever service dog litter. Given to Simon to help him manage his anxiety, Hercules quickly becomes a loyal and constant companion. He accompanies Simon everywhere, helping him face public spaces and difficult anniversaries.

Ms. Snodgrass is the principal of the junior high/high school in Grin and Bear It. She reviews Simon's file upon his arrival and later addresses the student body during a school assembly. She attempts to maintain order among the students when they mock a memorial event.

Miss Rose is Simon's homeroom and English teacher. She is observant of her students' behavior and notices Simon's severe, fearful reaction to the school bell.

Kevin's mother is an employee at the Very Large Radio Telescope for the SETI project. She is strict regarding her children's academic performance and becomes highly stressed when scientists suspect they have received a signal from space.

Kevin's dad runs Hello Hello, a coffee shop near the SETI project. He is welcoming and kind, actively encouraging Simon to keep visiting the shop even when Kevin needs space to process complicated feelings.

Agate's mother runs a chaotic household with seven children and breeds service dogs and Angora goats. She manages the intense demands of the farm, from assisting with animal births to handling neighborhood emergencies in the middle of the night.

Agate's father is a truck driver who shares his daughter's inner strength. When he meets Simon, he kindly suggests that Simon permanently keep the service dog puppy they provided.

Mr. Bagshott is a neighboring farmer to the van der Zwaan family. He owns a large herd of emus and frequently has to retrieve them when they escape. He is highly protective of his property and unbothered by the scientific community, occasionally using his animals to chase scientists away.

Todd is the family's golden retriever and the father of Hercules. Though he possesses the mechanical skills of a service dog, he lacks the natural concern for humans required for the job and occasionally causes trouble by leaving farm gates open.

Pretty Stabby is a male peacock that came with the funeral home property when Simon's family bought it. Highly territorial, he attacks the screeching front gate whenever it opens and occasionally chases away unwanted news reporters.

Kevin's sister is a minor presence in the Matapang household. She adopts their mother's strict view on education, ensuring her brother stays focused on his science fair projects and homework.