An odd thing just happened. I imported some images into LR 4 last night and edited a few of them in the develop module. Today I went back to these images and three of them were missing form the catalog -- no question marks, no place holder in the grid - just gone. The files and the .xmp attachments are still in the folder on the disk, and show up in Bridge. It's as if I removed them from the catalog (I don't think I did).
The question is, how do I get them back?