Egan is a young boy visiting his relatives in the town of Instep to attend the annual fair. Caught between his practical upbringing and the pervasive superstitions of his aunt's household, he questions the local legends. Naturally curious but sensitive to criticism, he feels pressured to prove his bravery when faced with his cousin's teasing about the mysterious creature on the mountain.

Ada is Egan's cousin, a stern and intense girl who deeply enjoys the fear surrounding local legends. She presents a hostile front to Egan upon his arrival, taking pleasure in the fact that her pet scratches him. She fully embraces the town's superstitions and frequently uses the terrifying myths of Instep to tease and challenge her visiting cousin.

Aunt Gertrude is Egan's aunt, a deeply superstitious and anxious woman living in Instep. She constantly worries about the unknown, heavily relying on rituals involving wishbones and onions to protect her household from the mountain's legendary creature. Her emotional inconsistency shows in how she quickly pivots from criticizing Egan to praising his cleverness.

Uncle Anson is Egan's uncle, a practical and calm craftsman who makes wooden clocks. Compared to his highly anxious wife and daughter, he maintains a more reserved demeanor during family discussions. Despite the pervasive local fears, he focuses on his craftsmanship, though his mechanical creations sometimes clash with the household's strict superstitions.

Uncle Ott is Egan's eccentric relative, a poet and traveler whose recent disappearance casts a shadow over the household. He left behind a room full of books, quills, ink, and his loyal dog, sparking intense fear among the family that he wandered up the dangerous mountainside and met a terrible fate.

The Megrimum is a mysterious entity rumored to live at the rocky peak of Kneeknock Rise. The creature is known for emitting a sound of tragic sadness during stormy nights. The townspeople of Instep deeply fear and revere this being, refusing to climb the mountain out of respect for its presence and their own superstitious traditions.

Annabelle is Uncle Ott's loyal dog, left behind at the house when he disappeared. She is a visually striking animal with a white coat that turns brown around her eyes, giving her a quizzical expression. She is friendly and welcoming, quickly forming a bond with Egan as he settles into his missing uncle's room.

The Cat is Ada's ill-tempered pet who shares its owner's immediate dislike of Egan. According to local superstition, felines are the Megrimum's favorite animal and receive special privileges. This belief explains the family's tolerance of its destructive behavior, particularly its aggressive attacks on Uncle Anson's mechanical birds.

Egan's Mother is a pragmatic woman who sends her son off to the Instep fair. She holds a critical but encouraging view of the trip, pushing Egan to appreciate the opportunity to visit his extended family despite his clear reluctance to stay with his nervous relatives.

Egan's Father is described by the relatives in Instep as a large, loud, and cheerful man. Though he does not accompany his son on the journey to the fair, Egan keeps him in mind and intends to purchase a souvenir to bring home to him.