The beginning of the end.

When they had decided to visit again Gravity Falls, Mabel had hoped to spend a joyful summer along their old friends, leaving apart the City's horrors and mysteries . Sadly her hopes are soon shattered against the harsh reality : When her brother disappear , everything starts to fall around her . The girl will be forced to face the terrible secrets that hide behind the city, and when a certain demon make his return, Mabel finds herself willing to do anything in order to fix everything and bring her brother back.
How much will she sacrifice?