The stars of Mount Quixx

Constance and Ivory Ivyweather are complete opposites, so they aren't happy to be sent away for the summer by their indifferent parents to the decaying town of Quixx that's covered by a mysterious fog that never seems to lift. The sisters soon meet Derrek, an astronomer who also happens to be a spider-like creature with a scientific mind and a tragic past, and they learn of the monsters who lurk in the shadows of the sleepy mountain town.