Rothgo

A sudden thunderstorm drives Terry and his sister Helen to shelter in a cave where they encounter another boy, Phil, and are led by mysterious cries for help to Rothgo, a magician from another time, who is trapped in the rock. He commands them to release him and asks them to enter a labyrinth leading to different points in time. He wants them to regain his focus of power, the Nidus, otherwise he will die in the caves as the evil witch Belor, who took the Nidus from him, intended.