Reunited with the mother she never knew, Mandie Shaw (Lexi Johnson) lastly has the household she constantly desired for, up until Uncle John intimidates to tear everything apart to keep an old assurance. After he restricts Mandie from joining his quest, Mandie and her friends start a traumatic trip by train to safeguard Uncle John. Grand adventure follows as they struggle to fix riddles as well as risk to encounter the secrets of the Lost Horn Cavern Mine. Bases on the series by Lois Leppard, this sequel to Mandie as well as the Secret Tunnel consists of an unique look by Hayley Mills.