Escape by Unicorn

Fourteen year old Aideen is horseback riding with her cousins on a picturesque mountain trail in Ireland. Near the summit, her horse rears and jumps into a pile of boulders which was, in times past, an ancient Irish tomb. Aideen is transported through these stones to the 5th century and finds that her "horse" is in reality a unicorn who had run away with her. Aideen's freedom and very life are in danger. How will she escape? By unicorn, of course