An E.Q.U.E.S.T.R.I.A Spies story

Lightning Star and the seven Rainbooms, Twilight Sparkle, Sunset Shimmer, Rainbow Dash, Applejack, Fluttershy, Rarity, Pinkie Pie, find something very mysterious about a tree located beneath an abandoned graveyard in their local school forest. It seems to have their names inscribed on it. So, after activating it with their magic and going through the archway, they find themselves transported to a FOURTH world, and caught up in a battle to save the Great Forest of Caisar from the wicked witch, Hexia- who has stolen all the power of Merrdom and the Islastone- a magical stone that is essential to keep the forest alive. Prince Dalton, the girls and the forest must face Hexia and her army of Cropers and Harats, to restore the world to its rightful place.