In the 1920’s, Mr MacDowell, a gifted astrologist, entered his new home where he immediately detected a surnatural being. Gathering eminent mediums of his time for an extraordinary seance, they will have 7 hours to contact the ghost and investigate to unlock an old mystery.

In Mysterium, a reworking of the game system present in Tajemnicze Domostwo, one player takes the role of ghost while everyone else represents a medium. To solve the crime, the ghost must first recall (with the aid of the mediums) all of the suspects present on the night of the murder. A number of suspect, location and murder weapon cards are placed on the table, and the ghost randomly assigns one of each of these in secret to a medium.