* Joe: Sarah Jane's younger brother, who is 10 years old. He is often the voice of reason for Sarah Jane, and is very loyal to her.
* Mr. and Mrs. Reed: Sarah Jane and Joe's parents. They are loving and supportive, but are also very busy with work.
* The Mysterious Stranger: A man who appears to Sarah Jane and Joe on their way to Last Man Peak. He gives them a warning about the dangers that lie ahead, and gives them a map to help them find their way.
* The Mountain Monster: A creature that Sarah Jane and Joe encounter on their journey. It is a large, hairy creature with sharp teeth and claws, and is very dangerous.
* The Spirit of Last Man Peak: A spirit that appears to Sarah Jane and Joe at the top of Last Man Peak. It tells them that they have completed their journey, and gives them a gift.