Heather

Heather is a side character/villain introduced in episode 110 of Riders of Berk "Heather Report, Part 1".

Heather was found by Snotlout and the other teens on Thor's Beach in a washed up ship wreck. She claimed to had escaped a siege to her home island and that her parents weren't so lucky when their ship was overrun with pirates.

As of being rescued by the teens, Heather had taken residence at Hiccup's home, sleeping in his room while he and Toothless sleep downstairs, as was planned to stay there until they could find a "safe place for her to go".

Playing in well with her beauty, knowledge of making saddles, and eagerness to learn about dragons, all the boys on Berk seem to be  immediately enamored with her--even Hiccup--willingly telling her all they know about their individual dragons and trying to win her over in the process. Heather used that control very well, skillfully manipulating them into doing and saying anything she wanted them to, and caused quite a bit of drama between Hiccup and Astrid "complicated friendship" (as stated on the Riders of Berk Facebook Page).

Heather reading the Book of Dragons

Despite her facade, Astrid is able to see past her front when she was caught by her reading the Book of Dragons in Hiccup's room. That still, though, wasn't enough to get anyone to believe Astrid's accusation that Heather was a spy and didn't stop Heather from trying to cajole Stormfly into befriending her and earned the dragons trust.

It was finally revealed later in the episode that Heather was, in fact, not who she wass letting on to be and was working as a spy for the Outcast, sent to the island via blackmail to learn all there is to know about Berk's dragons and report back to Alvin. Heather was after the book, though, claiming it would make Alvin "very happy".

Heather and Savage making a deal

No one was able to catch onto her--other than Astrid who, sadly, no one still believed--until she disappeared after making off with the Book of Dragons on Stormfly to Outcast Island. Though she didn't personally deliver the book to him, Alvin does get the book and Heather is 'saved' by Snotlout after being knocked off of Stormfly by Astrid.

After being rescued, though, Heather was taken back to Berk and locked up--apparently with the okay from Stoick--in Berk's prison chambers.

She frequently tried to escape and made many close attempts to do so but was also found by someone and taken back to her cell. Heather pleaded, specifically to Astrid, to let her go and finally revealed the true story that Alvin was the one who captured her parent, not pirates, and that is she doesn't go back to Outcast Island he'll kill them. Unfortunately, no one believed her at that point.

Heather in Berk's prison

After the group went off to retrieve the book from Alvin, Heather was able to sneak away and fly Stormfly--who was left because Astrid went to Outcast Island by boat disguised as Heather--to Outcast Island to retrieve her parents and when she got there she was able to assist the riders in fighting off the Outcasts and save her parents.

She was able to leave from Berk on a boat with her parents safe and sound back to their island and thanked Astrid for risking her life to save her parents. It seemed as though Astrid and Heather finally made it to a friendly impasse before she left, and even on Outcast Island Astrid apologized for not believing her.

Still, it seemed that Heather didn't return Hiccup's slight feelings for her, as for when he gestured for a hug she wordlessly turned him down and pet Toothless instead.

She also rejected Snotlout's want for them to write to each other as she left.

Heather saying Goodbye