I was at Bloodmoon Island, not a tag-granting-villain in sight (I tend to kill villains).

However, I ended up using a guide to edit save games:
http://larian.com/forums/ubbthreads.php?ubb=showflat&Number=605573

And digging through my save file, I found my character and replaced its Barbarian tag with a Scholar one - and I now have access to it all. Here's hoping it won't come back to bite me in the arse.