Reunited with the mother she never knew, Mandie Shaw (Lexi Johnson) finally has the family she always dreamed of, until Uncle John threatens to tear it all apart to keep an old promise. After he forbids Mandie from joining his quest, Mandie and her friends embark on a harrowing journey by train to protect Uncle John. Grand adventure ensues as they struggle to solve riddles and dare to face the secrets of the Lost Antler Cave Mine. Bases on the series by Lois Leppard, this sequel to Mandie and the Secret Tunnel includes a special appearance by Hayley Mills.