* David: The protagonist, a troubled and lonely teenager who discovers the time-traveling device.
* David's Mother: A loving but sometimes overprotective mother who struggles to understand her son's behavior.
* David's Father: A scientist working on a mysterious project who seems distant and uninterested in his son.
* Mr. and Mrs. Johnson: David's friendly neighbors who are also aware of the time-travel device.
* Mr. Sweeper: A mysterious and menacing character who seems to be connected to the time-travel device.
The book doesn't have many secondary characters, as the story revolves around David's journey and experiences with the rewind device.