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.
Siblings Grant and Christina embark on a journey westward aboard a covered wagon with their grandparents, Mimi and Papa, to follow the path of the Oregon Trail, but along the way, the family encounters a mystery amidst their adventure.
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.
Mimi is a mystery writer who travels the world with her husband, "Papa," and their grandchildren Christina, 10, and Grant, 7. In Pyramid, the four travelers arrive in Cairo and are immediately thrown into a sinister mystery involving gun-toting thieves and deadly threats. The children are pursued by would-be tomb robbers and help solve the mystery when they run straight into the arms of Papa and a policeman. In Colosseum, Christina finds a mysterious message in a newspaper and immediately notices men in black trench coats everywhere.
