Pandora Hearts ~Caucus Race~ is a novel written by Shinobu Wakamiya and illustrated by Jun Mochizuki. The plotline was meant to focus on all four dukedoms, portraying them in a fairytale-like manner. It tells about the many things that happened in the Four Dukedoms and how the characters dealt with them. Caucus Race also came with an all new Pandora Hearts one-shot.

(Source: Pandora Hearts Wiki)