In this National Parks Mystery, twelve-year-old Jack Landon and his younger sister Ashley travel with their wildlife biologist mom and photographer dad to Utah's Zion National Park. Dr. Olivia Landon becomes involved in an investigation into the strange behavior of a group of wild white mustangs that belong to the Chloride Herd. Trouble seems to follow the two yong Shoshone kids temporarily placed in the foster care of the Landons. A string of life-threatening disasters keeps young readers turning pages as the fast-paced story builds to a heart-stopping conclusion.