Mystery House is a monochrome interactive fiction adventure game that places the player in a Victorian mansion with seven other people. As the player explores the mansion, he discovers that there is a killer murdering each guest one by one. The objective of the game is to figure out who the murderer is before the murderer finds the hero. Players explore and manipulate objects by typing in one or two-word phrases such as "north" or "get knife".
Mystery House is an adventure game released by On-Line Systems in 1980. It was designed, written and illustrated by Roberta Williams and programmed by Ken Williams for the Apple II. Mystery House is the first graphical adventure game and the first game produced by On-Line Systems, the company which would evolve into Sierra On-Line. It is one of the earliest horror video games.