Dipper Pines and Mabel Pines have their own children with 20 years passing, Mason (Dipper's Son) and Mya (Mabel's Daughter), During living in Gravity Falls, Oregon, they meet and old enemy Bill Cipher but they have friends to save the day.

Mason and Mya's Parents dropped them off at Gravity Falls, Oregon, a place where wonder and mystery and including evil lives Bill Cipher is brought to life and he finds that Mason is Dipper's Son and Mya is Mabel's daughter he has a hatred towards him and Bill decides to destroy Mason and Mya.—Anonymous