The Pony and the Haunted Barn (#36 Pony Pals)

Pam and her Pony Pals have found the perfect new hideout...or so they think. The mysterious barn they discover while exploring a new trail in the woods near an old ghost town turns out to be creepier than they thought. Something unseen trips Pam's Pony, Lightning, a chain rattles, the door bangs shut, and a storm blows in out of nowhere. Not only that, the girls can't seem to find the barn after that day---though they are sure they are in the right spot. The ponies are frightened. Do they sense the presence of something the girls can't see?