Book 4 Abnaxus home Warning before entering Abnaxus home be sure to speak to the girl outside of the Fingerlings cart, you also need to speak to her once you leave the house and the fingerling show is over for the Prophecies Achievement
I would also recommend getting the Dirty Dancing Achievement before entering Abnaxus home although you can get it after. However the girl must be spoken to twice, once before the home and once after the puppet show. I missed this my first time.
After using the key to enter Abnaxus home. Run forward and interact with a book.
Brian will appear and QTE will occur, you can be honest or vague with Brian. I was vague.
After the cutscene with Brian run upstairs. On the right side of the bed is a row of books on the floor. Run into the crevice and you will see a piece of paper in between the books. Pick this up and take it to Brian and the achievement will unlock.
you are unable to pick up the note until after Brian appears.