MIsts of Darkness-Book Two of the Mist Trilogy

Having braved the evil powers in the Dark Kingdom and rescued a lost soul in Behind the Mist, Nick and Jazz proved themselves worthy to become members of the Legion of the Unicorn, the guardian angels to the animals on earth. In a ceremony passed down through the ages, Jazz is endowed with a glowing horn and a new name: Lazari. Nick becomes his partner as the first unicorn rider.
However, the celebration is short-lived as word reaches Celestia of an ominous dark mist that descended upon the ...