With your back to the double doors, turn right and pick up the bright blue HISTORY BOOK from behind the white pillar. Go up the spiral stairs behind you in the left corner of the room. Go left and forward to the bookcase with bright blue books. While holding the blue book you found behind the pillar, click on the book on the second row, right side. The bright blue History book will properly store itself and you'll have a bright green RELIGION BOOK in your inventory. Aha, so that's how it works. Let's repeat this exercise a few more times, tidy up the library, and maybe find a clue or two to Montcalfe's disappearance along the way.

Find the bookcase with bright green books. Exchange the green book while picking up a bright red GEOGRAPHY BOOK. Go back down the spiral stairs and over to the far left corner of the room (from the stairs) where you'll see the bright red books. Replace the light blue PHILOSOPHY BOOK with the red book. Sherlock just may be a victim of obsessive compulsive disorder, don't you think? Or maybe he missed a greater calling as a librarian?

Now, holding the Philosophy book go to the other end of the room in the right corner opposite the spiral stairs. On the second shelf of the bookcase, with the blue books, exchange the one you are carrying for the black LAW BOOK. Take the black law book back up the stairs till you're facing the bookcase with all black books. Exchange the one you have with the yellow SCIENCE BOOK on the right side of the second shelf. Now, go back down the stairs. Go slightly right and forward to the yellow books. Exchange the yellow book with the white PHILOSOPHY BOOK on the left side, second shelf. Exchange this philosophy book with another large white (may look blue) book in the third shelf, right in the middle. It's within this philosophy book that Sherlock finally finds what he didn't know he was looking for.....another KEY!