After the rain, there's no rainbow. Color is draining from the world!

Shiny Fluffy Hooves gets a new diary for her birthday, just in time for the worst thing that's ever happened in Glitterville. Some creature steals the rainbow from the sky, and Shiny is determined to get it back. All the clues lead to a dragon's cave, but the dragon, Razz, swears he didn't do it. Shiny sets out alone to find the real thief but is soon joined by Razz on her adventure. Shiny wants to save the world. Razz wants the gold at the end of the rainbow. Can a sparkly unicorn and a fire-breathing dragon work together to find the rainbow before it's too late?