New Episode of Dragons: Riders of Berk - Heather Report Part 2 on:
http://www.watchcartoons.tv/category/comedy/dragons-riders-of-berk/

Heather's betrayal to Berk caused the Book of Dragons to fall into Alvin the Treacherous' hands. In order to get the book back from Alvin, Astrid disguises as Heather and goes into Outcast Territory. Towards the end of her mission, Astrid learns and confirms Heather's true motives for serving the Outcasts.