Who was that man in the Park Service uniform who brought Jack and Ashley Landon into the wilds of Alaska’s Denali National Park along with their friend Nicky Milano? Whoever he was, he has given them a dogsled ride to certain death unless somebody finds them soon. Their troubles are about to get a whole heap deeper as the first rumblings of an avalanche turn into a deafening roar!

While their parents study why wolverines are disappearing from Alaska's Denali National Park, Jack and Ashley are stranded in a remote area with their mysterious new foster brother when a hit man's bullet triggers an avalanche.

A baby whale is the latest mammal stranded on the beaches of Acadia National Park. When the Landons run to get help, they don’t notice Bindy Callister slip away. When they track her down, she’s acting strange—she knows the strandings are no accident. She even knows those responsible. But she’s too scared to tell. Time is running out; and now the kids too are in real danger—unless Bindy talks!

The Landon family makes a trip to Death Valley National Park accompanied by a mysterious new foster child, fourteen-year-old Leesa Sherman.

The Landon family is Southbound—headed for Florida to investigate a mysterious illness plaguing endangered manatees in Everglades National Park. Jack, Ashley, and their friend Bridger soon find themselves in deadly waters with a seven-foot shark, an injured manatee—and a mystery to solve. Who was the stranger in the speedboat who snatched Jack's camera? And what does he have to do with the manatees? Join the heart-stopping chase through a maze of mangrove islands to find out!

Grizzly cubs are disappearing from Glacier National Park, and the Landon family must figure out why! But for Jack, the real mystery is his sister Ashley's strange behavior. What was she doing alone in the woods so early in the morning? And why did she lie to their parents? Jack's efforts to unravel the truth lead to a pulse-pounding adventure that brings the Landon kids face to face with an enraged grizzly—as Jack and his sister suddenly become the hunted.

While she studies condors in the Grand Canyon a scientist's life is threatened, and the strange, hostile, teenage computer whiz in her family's foster care might be involved.