The peace and harmony of Equestria is shattered when a mysterious foe attacks Canterlot. This evil warlord is able to defeat Princess Celestia and even the Elements of Harmony in one fell swoop, leaving only Luna to escape. With her throne lost and her allies defeated, Luna must find a way to rescue Equestria and her friends.

Cover art is not mine. this is the artiest who made it http://theomegaridley.deviantart.com/art/FoE-Canterlot-398487935

Disclaimer: Written before Season 4, so no tree of harmony