When Jupiter Redwood is sent to Gravity Falls to spend the summer with her great aunt Lenzee, she leaps at the opportunity to finally prove to her parents that monsters and legends exist. She can hardly believe her luck as she meets a pair of twins, Mabel and Dipper Pines, who seem to know everything there is to know about the sleepy old town. Despite the strict rules of her relative, Jupiter finds a way to explore and discover fantastic creatures and hidden secrets. As things go from spectacular to spooky, Jupiter discovers she might be in over her head. It's up to her and the Pines twins to uncover the truth and hope it doesn't put an early end to their adventures.

Arlynzaelia Redwood has many secrets, most of which would be considered dangerous. Her family is aligned with demons that grant them magic, in return for their loyalty. Arlyn, however, is determined to bring about the end of this deal, and the arrival of a familiar face in her hometown of Gravity Falls brings promising support. Things seem to be going well, until a newer evil arrives, one that Arlyn can't quite put her finger on. Will she be able to protect those she loves, or will the world come crashing to its knees?