Carol Peterson Book order

Bernie Banks, Cecelia Cornwall, and Roger Duncan have only just discovered the existence of the secret world of Belleterre--and that they are from it. Now they must set off to stop archaeologist Dr. Peter Potstop, who is determined to destroy Belleterre and endanger the surface world.Can the three kids save the world--again?Can they master the Belleterrean technology they don't understand?More importantly, will they ever get to finally understand what it means to be part of a family?The race is on!