Mimi tells Christina and Grant a ghost story that takes place in Death Valley, based on Aunt Erin's childhood experiences with her family on a road trip and a creepy castle.
Christina and Grant travel with Mimi and Papa to Devils Tower in Wyoming and get caught up in a mystery involving Native Americans, dinosaur fossils, unidentified flying objects, and more.
Christina, Grant, Mimi, and Papa visit the world-famous Hershey Chocolate Factory on the 100th anniversary of the founding of the town and quickly become involved in a mystery involving stolen silver dollars.
While researching one of Mimi's books in Detroit, Christina, Grant, Mimi, and Papa stumble upon a Motown musical mystery concerning classic cars, missing melodies, puzzling clues and lots of good music.
