From the Chaosium website:
Two Adventures Concerning One Disturbing Institution
When you think of a traditional game of Call of Cthulhu one element probably comes to mind – Sanity Checks. Beginning the scenario with a sound mind, characters progressively find themselves face to face with unspeakable terror that cause them to test their sanity. If their mind fails them, their characters become mentally unstable.
Ravenstone Sanitarium offers an alternative style of play to Call of Cthulhu. They will have control of three or four very different characters. Each character represents a different part of the main character’s mind due to multiple personality disorder.
After players make a Sanity check, a Personality Check is made as well. This decides which personality has suddenly taken control of the body. At that point, the players set aside their current character sheet and pick up the new character sheet.
The first of two scenarios will place the players in the heart of a mental hospital having lost all memory of who they are or where they came from. They must investigate the dark and very disturbing facility to discover who they are, but they may accidently uncover the truth behind Ravenstone as well.
Scenario number two returns to the sanitarium ten years later. New ownership has changed the operations, but a dark cloud still looms over. Players must discover what lies behind the illusionary curtain and shut the hospital down once and for all!