Constantinople is a player driven collaborative storytelling roleplaying game where the players take on the role of a carnifex- a professional monster hunter blessed with a supernatural power but doomed by its accompanying stigmata. They are forced to exterminate monsters on behalf of the empire for a few  gold solidi.

The core game loop revolves around being given a mission from a magus regarding evidence of monstrous or supernatural activity. They investigate by examining bodies. following tracks and interviewing witnesses until they have enough clues to work out what monster they are facing. Once they have correctly identified the monster they can track it to its lair and either kill it, drive it off, bargain with it or decide its harmless and leave it alone.  They way they deal with the monster grants them increased reputation with the imperium, the proletariat and the magical community. They can use this improved reputation to upgrade their equipment, spells and alchemical devices.

The mechanics of the game favour a low pre-approach on behalf of the narrator. Players are encouraged to do most of the inventing and talking. They are able to create elements of the narrative as they go along and bring them into being to aid their investigation. Being an ex-soldier allows a character to create a military veteran for example. The character's player comes up with a name, appearance and how they know them. The narrator then takes over and describes what help the veteran is able to provide.