Ok, the Intellect Devourer escaped me, saying something about not wanting to be trapped/confined/something. No big deal, I figured he'd be running around the prison somewhere and I would finish him off then. One problem, I can't find him.

Is there some place that he always is?
Or does he wander around and I have to just find him somehow?
And if so, where does he wander?
Or, is it a bug and I won't find him and I am screwed?

Have you checked every where on the level where he is. He may be in a corner somewhere. Or, as you said, it may just be an unfortunate bug.

There are some bugs around the intellect devourer. You should have the latest patch installed, since it fixes it.

Heh, this happened right after I installed 1.28. But it doesn't matter now. I started playing the Witch's Wake module when I accidently hit quicksave, thereby erasing what I had done. Normally that wouldn't really have been too much of a problem since I do regular saves every so often. But I think I just plum forgot, now I have to start Chap One over again. But thanks to both of you for answering.