"Part 4" is the fifty-third issue comic book series The Unwritten, and the fourth issue of the five-issue crossover event The Unwritten Fables, released on September 25, 2013.
Publisher's summary
As "The Unwritten Fables" continues, it looks like the darkest hour, but somehow things continue to get darker. Nothing stands between Mister Dark and the endless, nested worlds of reality and story—except a witch without a conscience, a prince crippled by grief and three schoolchildren who are starting to realize that they're wearing the wrong faces.