"So it is told that long ago when the world was younger and the rulers of men were different, there were two courts, and they were named for the places where they made their homes, Great Oak and Berry Forest, for in those days no two courts would share a forest, or a valley, or a bend in a river, and every court claimed more land than they could surveil, imagining that this would make them great and knowing rightly that it made them more able to gather food when it was scarce. And they dealt with trespassers lightly, as they could not prevent them and cared not to negotiate every passage through each others' land, and debts grew up between them but not with either court ever too far above the other, and so they thought they were of no concern.
And then one faery of the court of Great Oak, called the Traitorous, tired of his obligations and slipped away in the night, and left the Misty Isles entirely to wander other isles, and his court was confused but did not seek him very far, and barely noted that he'd been much in the debt of the other court for his trespasses.
And at some other date, two faeries of the court of Berry Forest left, and it's not known where they went and it can only be inferred what they did there.
Winters passed, and the court of Berry Forest started to experience ill fortune. Lightning struck and killed someone, and they thought that perhaps he'd spoken unwisely - which shouldn't have done it, with no one to hear it, but they didn't know that. Then plants got sick, and shriveled over the course of days, and died. Then a boar crashed through the forest, killing many other plants, and was killed itself, and attracted scavenger animals, and the bush ravaged by these events. And they said that it might have been coincidence, but the court of Great Oak decided to settle all its debts, and track them more cautiously in future, and brought many gifts to assist their friends, and then got loose of them.
Things got worse. A storm came, and lingered, and flooded the ground higher than it had ever flooded, and forced the people of Berry Forest to retreat up a tree, which was then struck again by lightning; the survivors found themselves sick in the way faeries are seldom sick, too hot or too cold, with strange rashes on their skin; many of them found that they could not speak, and those who could speak could not sleep, and found themselves slowly mad from it.
And for Great Oak, too, things went ill, though more subtly; they were only sure of it when a great mathematician who engaged in gambling games with his friends from other courts came home with a great proof that the court's fortune had turned for ill, and was still turning. They found that the wood of their tree was infested with termites; they sought out other locations and found them wilting or inhabited by animals; a deer came by and ate all the flowers. And they questioned their own members, and sought out members who'd been lost, and then someone remembered that the Traitorous had been entangled with Berry Forest, and was, somehow, not yet dead.
So then they searched for him in earnest, and gave away all that they had to other courts in exchange for help or advice or just a promise to hold the Traitorous if they saw him, and in desperation promised their sons and daughters for favors, and they tracked him across his island and found him, feverish and lost and clinging to life in a rock cave to the far north, unsure what had happened to him, and they killed him and their ill fortune broke and they spent many long centuries recovering."