Seventeen-year-old Meridian Page has a rich imagination. To escape her quiet and boring town of Biddleborn, she makes up stories in her head—stories about a magic-filled world called Detritus and its inhabitants, including a princess named Lanora and a man called the Cat Lord. Not realizing how thin the walls of reality can be in a town where children have nothing better to do than tell stories, Meridian is shocked when the Cat Lord shows up in Biddleborn and warns her that imaginary characters like him are slipping through from Detritus to the real world.

With a doorway from the imaginary world of Detritus open, Meridian's imaginary characters—talking lawnmowers, a friendly skeleton, mutant animals and other creatures, living appliances, a wise dragon, zombies, dangerous creatures called shadow wights, and more—are increasingly slipping through to Biddleborn. By the time other Biddleborn residents' imaginary characters begin showing up as well, the town is awash in chaos as evil characters battle good ones and the town's residents. Can Meridian, her friends Artie and Cheese Fry, their parents, and Biddleborn's other residents save the town from Meridian's imagination? Read and find out.