From the module:
The forces of nature have formed a barricade around an ancestral home, not to prevent intruders but instead to keep something inside from getting out.
They say the god of nature never forgets. This deity, known today as Oon, birthed himself from nothingness by planting his own seed among the stars. His first memory was of his roots sinking deep into the cosmos, stealing secrets from the place before Time began. Millennia later, one of his clerics would try in turn to steal from Oon, and the god punished the man by transforming him into a deathless creature, forced to live in misery for eternity. Yet in his wisdom, Oon did not permit his fallen priest to roam the countryside freely and write terror in the hearts of the undeserving peasants. Instead, the very plants were commanded to imprison the undead forever.
Of course, that entire story is nothing but a tale told by old wives. Here is what is known as fact: A once-imposing residence called Coltherstone Hold was abandoned years ago, and in the decades since, a fantastic amount of vegetation has grown up the walls and rooftops, covering the structure. Many of the plants are dangerous—deadly, even—and reclaiming the Hold will require more than just a few machetes to chop down some weeds. Much worse, a few of the plant specimens possess intelligence as well as an undo degree of malevolence, and they’ve infested a nearby village, all but burying it in overgrowth . . . and absorbing a few villagers along the way.