After 10 years away from Gravity Falls, Mabel Pines gets a call beckoning her back to the twin's old summer home. Mason Pines begrudgingly obliges to follow her after tragic events following the success of his writing career. The two are soon to discover that the Falls is not nearly as wondrous as their 12-year-old selves believed. Their paths to find magic are coated with horror as they seek out the truth behind their grand uncle's death. Through hidden trails and unknown technology, the fantasy previously known to their sleepy Oregon town has been disrupted in favor of controlling the world. In the end, they will find an old friend who was eagerly awaiting their return.