After Dipper's and Mabel's parents got divorced and their father moved away because of his new job in LA ,their mother decided that a fresh start would help the family to recover . They're moving away from Piedmont, back to Gravity Falls . The twins are 14 in the beginning of the story , which starts in end of the summer holidays . With dimensional rips , occasional monsters and an emerging society trying to free the all known chaotic demon Bill cipher the twins are facing many problems but now with the beginning of high school Mabel and dipper are facing a new problem. growing up .