This adventure was originally released about the same time as the Psionics Handbook, and so provides an opportunity for a character who wishes to develop psionic powers to play out how he came to have them.
The background for the DM tells of how one Lord Prisius has a rather unusual castle with interesting architecture... and that his young daughter is the architect! Only one night the young lady vanished, and her father is offering a reward to anyone who can explain what's happened to her or, even better, bring her back. Enter the party... The background also explains what is really going on, of course.
The adventure involves a lot of interaction and investigation, meeting the various inhabitants of the castle and figuring out what has actually taken place. Once you have got the party involved, they may wander at will around the castle and surrounding lands. A series of encounters are provided, but they may be run in any order depending on what the party chooses to do and where they decide to go. The DM is provided with a list of 'Secrets' and it's made clear who knows what, role-playing will be needed to find out what each person knows - and if you wish to roll for NPC attitudes, their knowledge is differentiated as to what they are prepared to reveal depending on whether they are indifferent, friendly or helpful (along with the DC checks to get them there). A good map of the castle is provided too.
There is quite a good possibility of a fight at the very end of the adventure once the characters have figured out what is going on, but the rest depends on wits and role-playing rather than combat skills. The adventure will probably work best in a world where there is some but not much psionics, and it would be possible for the party - if astute - to figure things out even if none of them are gifted in that direction. However it would provide an excellent opportunity for a player who wants to develop his character's abilities in psionics to take the first steps as his gift slowly burgeons... talk it over out of character with your players in advance and if someone is interested in developing psionics, this adventure can provide the opportunity for his journey to begin.