David K. Anderson

On Earth, Christy bides her time plotting to go back to the Empty World. She has the means; she just needs to round up as many friends as she can and convince them to go with her. All is not right in the Empty World, and Doug and Mike may not be able to defend the pyramid by themselves....

Lost technology might let him walk again, but he'll need lost friends to help him get home. Cory delves into the empty world all on his own with just a computer-generated guardian for an ally....

With the ever-faithful Trevor in tow, Christy defies her mother’s wishes and ventures back to the Empty World. Her father and Detective Lockhart have been missing for months, and she’s determined to bring them home safely....

A missing grandfather. Two missing friends. A forbidden rescue plan. Christy’s parents forbid her from returning through the portal, but her grandfather is still stranded in the Empty World. When Danny and Brad accidentally take a trip into the portal, Christy finds the excuse she needs to...

They said her grandfather was dead. They said her grandmother was crazy. Christy knows they're wrong. When her grandmother dies, 13-year-old Christy inherits an old family secret: The pond behind her house is, in fact, a portal to another world. What's more, she learns her grandfather went...