There is a secret in Nightmare's dark, stone brick castle. A lone chained and bolted door (only known to have a single key), dwelling far passed long, winding corridors and hidden deeper than the dungeon itself; A door that no one is allowed to go through.

Killer, however, finds it difficult to ignore the allure of such a forbidden place. Including the mysteries that lurk behind. There are too many questions surrounding the topic from him not to be hopelessly curious. For example: Why does Nightmare routinely venture beyond the door once or twice every week? What about the new moon leads the dark king to hole up in there until the next day? But, most importantly, what causes those sickening squishy noises on the other side?

The hoodie-clad murderer is determined to find out- answers to these questions and much more.

Unfortunately, it doesn't quite happen under the circumstance he desired. For when Dream's latest outlandish scheme to get his brother back takes a dark turn, it looks like not just Killer will be discovering the secret behind the door.

...The secret that may have been better left locked in.