"It's wet, it's loud and it's enormous! It's Niagara Falls! Grant and Christina can't wait to go on another trip with their grandparents Mimi and Papa. Mimi writes mysteries and mystery never fails to follow the kids wherever they go including this wild and wonderful place! Along with new friends Allison and David, Grant and Christina spy b-b-b-bouncing barrels, discover a secret room, visit a famous fort, ride a Ferris wheel (Wheeee!!!), learn about...

Christina, Grant, Mimi, and Papa travel to the Great Smoky Mountains where they are pulled into another mystery that combines confusing clues and the local folklore.

Christina and Grant team up with a pair of twins to investigate the disappearance of the Winter Carnival Medallion from the popular St. Paul festival.

When they take a tour of baseball's most famous places, Christina, Grant, Mimi, and Papa slide head-first into a baseball mystery.

Christina, Grant, Mimi, and Papa find themselves in the middle of a mystery in Death Valley, California. There's Aunt Erin, a creepy castle in the middle of nowhere, a ghost (or not?), temperatures hotter than a Fourth of July firecracker, and more!

Christina, Grant, Mimi, and Papa make their way to Mount Rushmore to check out the colossal carving of four presidents...and find a mountain's worth of mystery, history, precocious prairie dogs, quirky clues, befuddling Badlands, and one Crazy Horse!

Christina and Grant travel to Sochi, Russia, for the Winter Olympics and uncover a clue in a big fur coat and get separated from Mimi and Papa on a speeding train.

The kids find plenty of history, mystery, legend, lore, lost bones, and more when they travel to Jamestown, Va., the first permanent English colony in America.

Christina and Grant meet two new friends, Taj, and Mahal, when they visit the Taj Mahal, in India and things continue to become more strange as they spend more time there.