Taken to Antarctica by the man she thinks of as her uncle for what she believes to be a vacation, Symone--a troubled fourteen year old--discovers that he is dangerously obsessed with seeking Symme's Hole, an opening that supposedly leads into the center of a hollow Earth.

"The Austins have settled back into their beloved home in the country after more than a year away. Though they had all missed the predictability and security of life in Thornhill, Vicky Austin is discovering that slipping back into her old life isn't easy. She's been changed by life in New York City and her travels around the country while her old friends seem to have stayed the same. So Vicky finds herself spending time with a new friend, Serena...

The magic tree house takes Jack and Annie to Antarctica to search for the fourth secret of happiness for Merlin.