While on a mission, the Seaview appears to pass through an odd magnetic field. However, a dinosaur and alterations in the star patterns indicate that they have been thrown back in time one million years. Nelson encounters the mysterious Mr. Pem, a man who has learned how to control time, and wants to use the Seaview as a powerful source of energy for his time device. Nelson must try to outwit a man who can simply back up time and alter anything they attempt to do. (thetvdb.com)