For me, this was the second to last story achievement, but your experience may vary depending on how you tackle things.
You'll get this once you've progressed Ms. Charm far enough to go back to the Astrologer, and then he wants books. You'll give him a silver book one week, a gold the next (for a separate achievement), and on the third week come back with your Aristocrat Papers (that you needed to get further with Ms. Charm anyway). Once you do, you can trigger a cutscene with the Astrologer, Vagner, and Ms. Charm, and by the end they'll give you two of the six relic items you need to get home.