How will Demon, official Beast Keeper of Mount Olympus, heal a herd of sick unicorns before it's too late?

Demon has just returned from a trip to Asgard when a brand-new set of disasters fall into his lap. Not only does he have a groggy volcano monster to deal with, but something seems to be wrong with the unicorns, too. Demon's only clue is a mysterious note saying Unicorn Emergency! left on his bed. What does it mean? And how will Demon figure out the problem and fix it before time runs out?