When Finn breaks a promise he can't remember making, he is confronted by Chronologius Rex, the lord of Hours and All Time.
Finn's life will be consumed in the infinite first of the fourth dimension unless he and his friends back home can find the moment that explains it all and bring him back him back to Ooo.
Finn must confront the ghosts of his past selves, the alternate selves of his present, and all his possible futures, while Jake gather help from all of Ooo and beyond. Together, they must save Finn before he goes beyond the Vanishing point and is erased from every reality.