The plot of this story takes place after Race to the Edge, only a few months before HTTYD2. I want to say maybe a month or two before, being in the middle of fall, the movie taking place in late fall/early winter I'm guessing.
Chapter 1—Prologue:
Long ago, in an archipelago far off in the cold north, something amazingly extraordinary happened. At the very same moment, two identical baby girls were born. One, a baby princess; the heir to the throne of Berk. The Chief and Chieftess were so overjoyed. Hiccup may have been different, being born early and weak, not mention being part Night Fury, but they had faith she would become the strongest of them all one day saving their village from the raids that consumed them, and loved her all the same. The second baby girl was named Alva born early as well on an island a bit north from Berk. She too had dragon parts and scales, only being white instead, and her hair was a blond color as opposed to Hiccup's auburn. Her parents loved her every bit as much as Berk's Chief and Cheiftess loved their princess, but they worried. They were too poor to care for their little one. How would they do it?
Many years passed, and the princess lived a harsh life at first, losing her mother, followed by neglect and abuse from her father and the village for many years. Life got better for her though after meeting her Night Fury companion, Toothless, and she soon found herself with great friends exploring lands far and wide. By age 20, her father was so proud of her growth that she soon found herself in training for being chief working hard in learning all her royal duties; to say she wasn't thrilled was an understatement. Meanwhile, when Alva had come of age, she only worked long and hard as a seamstress in a shop for the spiteful Lady Brenna on an island that held the Northern Markets. It wasn't as exciting, but just as miserable.
With lives so different and so far apart, it wasn't surprising that the heiress and the pauper never met. But, fate decreed they would…
It all started at the mines on Berk when the miners informed the chief the gold had run out. Chief Stoick was in utter shock, and now Berk was in serious danger. With no gold they wouldn't last for too long; the harvest wasn't very good to them this year, and trade had become very slow since Johann's recent betrayal and death. Over the past few years the population of not only dragons but humans had increased. Finding a way to feed everyone was becoming harder and harder each year with just their normal means of providing alone, and as such they had become more reliant on buying and trading for goods since the war with the dragons had ceased.
He had held a meeting with the council trying to figure out a plan of action, but they were at a standstill. If only he could call on his old friend, Alvin; he might have had an idea. But he was away on a long journey and there was no telling where he was or when he'd return. He couldn't wait around for the Outcast Chief. He needed to do something quickly. But what? And then, looking at his daughter as she sparred with Aric Hofferson, a young solider in their guard, it struck him. Nearby, there was a rich young chief who was seeking a wife, and in just a few days he would be coming to Berk to form a brand new treaty.