What if Hiccup really did end up leaving Berk with Toothless in the first movie?
After Hiccup left Berk, he started to travel to islands surrounding Berk helping the dragons that lived there fend for themselves and get food.
A few years later, the tribe of Berk go to Dragon Island to have another go to find the nest. The nest isn't going to be the only thing they find.
(This book might run through the events of How to Train Your Dragon II).
[Disclaimer: I don't own anything in the How to Train Your Dragon franchise (movies, TV series or books). Also this book is a complete AU (Alternative Universe) of the first and second movie.]