When Nancy, Bess, and George continue their journey and board a train bound for Denali National Park, they become aware that danger has followed them and Nancy worries her undercover status has been discovered.
When his sister disappears, Noah, along with their best friends, Ella and Richie, sneak into the neighborhood zoo and delve into the unknown world of the animals, where they discover a great secret that the zoo is protecting.
When competition for lucrative prizes ranging from money to placement on the Olympic Team escalates to the point where one desperate participant drugs horses at the River Heights Horse Show, Nancy, Bess, and George track clues to identify the culprit.