From the publisher:
On a Moonless Night is a tabletop roleplaying game of occult investigation, horror, and collaborative storytelling. The game is intended to be played in one sitting, over the course of two to four hours, by two to five players - a group of Investigators and one Host, who runs the game, creates challenges for the characters, and narrates the horrors as they unfold.
The players take on the roles of nineteenth-century occult investigators, and the Host describes their journey into the lair of an unknown Enemy. The aim of the game is to help the whole group tell an engaging, surprising story about venturing into a terrifying location, piecing together fragmented clues, and confronting the evil found within. The story might end with the characters triumphing and banishing the evil from this world. Equally it might end with the investigators devoured, body and soul, by terror.