Colt in the Cave (Animal Ark Hauntings, #4) by Ben M. Baglio

A spooky spin-off of the best-selling Animal Ark series, this new Hauntings title will have animal-lovers shivering in fear and delight. Mandy and her best friend James are used to dealing with animals in distress. But ghostly animals in distress are a different matter... Mandy and James are excited about their school trip to an old mine. Deep underground, Mandy begins to imagine how difficult life must have been for the ponies that used to work down there. Suddenly, she spots eyes gleaming in the darkness, watching her. But James can't see a thing! The very next night, Mandy dreams about a troubled pony. What can it all mean - is there a horse that needs her help?