After saving the universe, Steven is still at it, tying up every loose end. As he runs out of other people's problems to solve, he'll finally have to face his own.
When the Boogey Man causes Grim to lose his powers, rank, and title in the Underworld Court for misusing his powers, he plots to seek out Horror's Hand and take over the world. It's up to Billy, Mandy, Irwin, and Grim to get to Horror's Hand before the Boogey Man does.
