Bill is upset that his cousin, Donnie, a bully, is being sent to live with them. During a short truce, Bill told him about his time-trip, (Time-Travel Runaway) using a device his mysterious neighbor had invented. Sparks fly when Donnie gets Bill into trouble at school. When Donnie feels threatened, he breaks in to use it to go back to the same period, 75 million years in the past! Bill tries to stop him and both end up stranded. If they can't work together to survive, things could end quickly! Bill's only hope is for his friend, Mr. Cromwell, to find out what happened and save them; IF they can stay alive until then!