Gravity Falls: Wills son X OC

Lore - Four years have passed since the twins went to go and stay with their Grunkle stan. Bill terrorized the town, drama with dippers emotions, and the author. But now the twins are 17, and much more mature than last time. Mabel who was getting ready to go to art school, and Dipper who was going to university to study astronomy. They both decided to take this summer to spend with family before they left to start off their life's. Originally the twins were to go to Europe with their parents, until Dipper received a letter from their Grunkle Ford. It was a terrible letter that was written with big, bold letters.

COME AT ONCE, GRAVITY FALLS IS IN DANGER!! WE NEED YOUR HELP, THIS MIGHT BE WORSE THAN BILL. - From Ford.

With that the twins, rushed off to gravity falls, hoping they could solve this mystery.