Glome's Valley — Peggy Chambers

When Ethan and his dad go to Heavener, Oklahoma to read an ancient runestone, he is sure he's going to be bored all summer. But Ethan quickly makes new friends -- so what if they're ghosts? What began as a trip to Dullville suddenly becomes a fantastic adventure. There are other creatures living in the valleys near the runestone -- energetic fairies, beautiful wood nymphs, and smelly old trolls. Ethan stumbles into the midst of an ancient war, and the only person that can save him is his archaeologist dad -- with a little help from Thor and the phone app that summons him.