Ed Boone, Christopher’s father, runs a small heating repair business. He struggles with personal issues but cares deeply for his son. Their relationship becomes strained as Christopher pursues the dog murder mystery.

Judy Boone is Christopher’s mother, who is lively and intense. She leaves the family at one point, which has a significant impact on Christopher's life and emotional development.

Siobhan is Christopher's tutor who provides guidance and support. She encourages him to write about his experiences, helping him to navigate his social world and cope with the challenges of Autism.

Mrs. Shears is a neighbor of Christopher and his father, Ed. She becomes indirectly involved in the dog's death mystery because of her connection to Wellington, the deceased dog.

Roger Shears is a neighbor involved in a complicated relationship with Christopher's mother, Judy. He becomes a part of Christopher's investigation due to his connection to Judy and Eileen.

Mrs. Alexander is an elderly neighbor who assists Christopher in uncovering local secrets pertinent to his investigation into Wellington’s murder.

Rhodri is an assistant in Ed Boone's business who sometimes interacts with Christopher, using his talent for arithmetic as a form of entertainment.

Toby is Christopher’s pet rat, which he dearly loves and cares for, representing an important part of Christopher's life and emotional world.

Sandy is the golden retriever puppy given to Christopher by his father after Toby's death, symbolizing comfort and helping mend the father-son relationship.

Wellington is the deceased dog, a French poodle owned by Mrs. Shears. Wellington's death is the central mystery that drives the plot of *The Curious Incident of the Dog in the Night-Time*.