Although this may have little bearing, it may spark some idea - what is Talos the god of?
As for hints, I'd leave the whole invisible thing a mystery, by this point, he'll be high enough level to be able to deal with it (and the mental test will be if he can figure it out). Instead, hint / clue the PC towards the tower itself. Let the PC rip it up looking for the item. While searing the tower though, there should be other items/clues that hint that the mage had planar activites - maybe very obvious spell components for plane traveling spells (if there are any - don't have the books handy) or even just lots of books on it the mage's library maybe even planar creatures in the dungeon.
(PS. only skimmed your posting so if something here does not make sense, that would be why.. apologies if I'm off
)
As for hints, I'd leave the whole invisible thing a mystery, by this point, he'll be high enough level to be able to deal with it (and the mental test will be if he can figure it out). Instead, hint / clue the PC towards the tower itself. Let the PC rip it up looking for the item. While searing the tower though, there should be other items/clues that hint that the mage had planar activites - maybe very obvious spell components for plane traveling spells (if there are any - don't have the books handy) or even just lots of books on it the mage's library maybe even planar creatures in the dungeon.
(PS. only skimmed your posting so if something here does not make sense, that would be why.. apologies if I'm off
)
