12 year old Mabel Pines takes her 7 year old younger brother Dipper with her to Gravity Falls to stay with their great uncle for the summer. She's starting to regret taking him along after he makes a not-so-imaginary friend.
Dipper Pines along with his twin sister, Mabel Pines, goes off to live with their uncle Stan and Ford. They been there since they were kids so it was like a normal thing but this time, it was permanent.
Their parents died in a car accident. Mabel decide that they are both gonna live in Gravity Falls. It was the summer and it's a great time to go since they go every year.
Dipper and Mabel are finally 18. The year they are gonna graduate. Before that, Dipper finds out that Mabel became friends with a triangle.
Mabel made a bet. A bet that could be true.