You decide that a falling stack of books is a less suspicious distraction.

After a quick look around the nearby aisles, you spot a pile of books tall enough to create a sufficient distraction - while also being close enough to an opening in the shelves for you to take cover after. Shooting one last glance at the feathered librarian, you give the stack a gentle push; it wobbles slightly, then begins collapsing into a pile of paper and leather binding!

CRASH!

You have just enough time to duck behind a pile of books in the adjacent aisle before the tower tumbles over. The harpy perks up, then sighs with quiet dismay as she observes the mess. She puts away her quill, then glides down the aisle next to you towards the pile of books - leaving the desk unoccupied. Taking your chance, you hurry towards the glass case as quietly as you can, leaving the harpy behind - rather than simply restack the books, she's begun to carefully reshelve them. All the better for you!

You quickly duck behind the desk to conceal yourself in case she happens to look your way. Now there's only the matter of the book itself... the glass case is obviously locked, and all the magic energy wrapped around it means the lock is likely enchanted. You could obviously try breaking the case open - but that seems like it would be a rather poor choice.

You could try unlocking the case with Strokmier - quietly, of course - and then steal the book. You'd prefer to have more time since it really isn't made for such precise work, but you think you could manage... or you could take the entire case and unlock it more carefully in the next room. The case seems rather heavy and the harpy will likely notice its absence, but it is an option.