gidgemuffin: there are a couple of keys in the cathedral that all open locks in the building. there is one on a table in the back room where Kimberlea is hanging out. (and grab the bottle of serpentwyne that is on the table as well) there is a button on a wall in one of the bedrooms--press it. there is another key that you should be able to find pretty easily after that.

1 more suggestion--don't bother collecting or carrying around bottles of serpent venom but you should definitely grab every bottle of serpentwyne you find!! you will have a couple of opportunities to increase your karma by giving away a couple of bottles but other than that, they can be invaluable for restoring mana and hit points when you are in a dungeon and can't rest.