Books in the Halcyon Cycle series

Albert Gleeson, his pregnant wife Pam, and his young stepson are struggling to adjust to their life on an acreage in Georgia after their return to our world. However, on his way home from a long day of teaching, Al finds that his home has been ransacked-and his family kidnapped. The police initially suspect him of foul play. When he's finally cleared, with the help of his friends, Al pursues the kidnappers to Abaddon, a continent whose main land surface rests ten kilometres below sea level.Their search eventually forces them to cross an even deeper abyss, called Sheol, where the air pressure is so high that dragons fly. Fighting frustration and despair at his inability to locate Pam and his stepson, Al soon begins to understand that he has a role to play in rescuing the enslaved prisoners of Abaddon.