At the Symbol Ceremony, unicorn foals get their symbols. Iris and Ruby perform the ceremony under the full moon for Starsong and Heart's Mirror. Afterward, Iris discovers a new unicorn is watching them: a unicorn with the marks of a dragon. According to legend, a unicorn born under the Dragon Moon will be cast out from the herd. But does Ember Shadow need to be an outcast? Can Iris help the other unicorns welcome him into the herd? 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.