Iris cannot wait for Heartsong to have her foal. Unicorns go into the Fairy Forest to have their babies, so Iris isn't surprised when Heartsong goes missing for a few days. Yet when the unicorn does not return, Iris and Ruby have to go in and find her. The Fairy Forest is filled with trickster magic and can be a dangerous place. Can Iris and Ruby find Heartsong and her missing foal before it is too late? There are unicorns behind Magic Moon Stable, but no one knows they exist except Iris and Ruby. As Unicorn Guardians, the two girls must protect the unicorns to keep them safe from the outside world.