1. Jack O'Reilly: Jack is a middle-school student who loves animals, especially dogs. He lives in a small town in New Jersey with his parents and his younger sister, Emily.
2. Emily O'Reilly: Emily is Jack's younger sister. She is a kind and compassionate girl who also loves animals.
3. Mr. O'Reilly: Jack and Emily's father. He is a veterinarian.
4. Mrs. O'Reilly: Jack and Emily's mother. She is a stay-at-home mom.
5. Shadow: Shadow is a stray dog who Jack finds and takes home. He is a black Labrador retriever mix.
6. Ace: Ace is the town dogcatcher. He is a mean and grumpy man who hates dogs.
7. Mayor Jenkins: Mayor Jenkins is the mayor of the town. He is a kind and compassionate man who loves dogs.
8. Mr. Jenkins: Mr. Jenkins is the mayor's son. He is a kind and compassionate boy who also loves dogs.
9. Mrs. Jenkins: Mrs. Jenkins is the mayor's wife. She is a kind and compassionate woman who also loves dogs.
10. Pepper: Pepper is the Jenkins family dog. She is a small white poodle.
11. Miss Barker: Miss Barker is Jack and Emily's fifth-grade teacher. She is a strict and no-nonsense teacher who does not like animals.
12. Mrs. Jones: Mrs. Jones is the principal of Jack and Emily's school. She is a kind and compassionate woman who loves animals.