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. Plot The game starts near an abandoned Victorian mansion. The player is soon locked inside the house with no other option than to explore. The mansion contains many interesting rooms and seven other people: Tom, a plumber; Sam, a mechanic; Sally, a seamstress; Dr. Green, a surgeon; Joe, a grave-digger; Bill, a butcher; Daisy, a cook. Initially, the player has to search the house in order to find a hidden cache of jewels. Soon, dead bodies (of the other people) begin appearing and it is obvious there is a murderer on the loose in the house. The player must discover who it is or become the next victim. Development and release At the end of the 1970s, Ken Williams sought to set up a company for enterprise software for the market-dominating Apple II computer. One day, he took a teletype terminal to his house to work on the development of an accounting program. Looking through a catalog, he found a game called Colossal Cave Adventure. He bought the game and introduced it to his wife, Roberta, and they both played through it. They began to search for something similar but found the market underdeveloped. Roberta decided that she could write her own, and conceived of the plot for Mystery House, taking inspiration from Agatha Christie's novel And Then There Were None. She was also inspired by the board game Clue, which helped to break her out from a linear structure to the game. Recognizing that though she knew some programming, she needed someone else to code the game, she convinced her husband to help her. Ken agreed and borrowed his brother's Apple II computer to write the game on. Ken suggested that adding graphical scenes to the otherwise text-based game would make it more interesting for players, and the couple bought a VersaWriter machine, on which users can trace over a line drawing and convert it to a digital drawing. Roberta drew seventy scenes for the game. Ken found, however, that the resulting digital drawings were too