Moonmist

Moonmist is an interactive fiction computer game written by Stu Galley and Jim Lawrence and published by Infocom in 1986. The game was released simultaneously for many platforms, including the IBM PC, Apple II, Amiga, Atari ST and Commodore 64. It is Infocom's twenty-second game.
Galley and Lawrence previously wrote Seastalker for Infocom.

The player's character is a young detective, asked by friend Tamara Lynd to investigate her new home of Tresyllian Castle in Cornwall, England. Tamara has recently become engaged to the castle's lord, Jack Tresyllian. She was very happy until she began seeing what appeared to be The White Lady, a ghost who has allegedly haunted the castle for centuries. As if seeing a ghost wasn't nerve-racking enough, she's also begun to fear for her life. Is Tamara's imagination just overly excited from living in a large old castle, or is someone really trying to kill her? And if her life is in danger, is it from a ghost or someone using it as a disguise?