You decide that a distant distraction should give you the most time to move in.

Searching the bookshelves quickly, you find and pull out a decently large, beige book. It feels hefty enough to be thrown a good distance and still make a nice loud noise when it lands. As long as you throw it far enough, the harpy shouldn't search your aisle. You step back a short ways and take aim over the shelf next to you, then give the book a solid throw! The moment the tome leaves your fingers you duck back behind the nearby stack of books, bracing yourself for the impact.

THWAP!

The noise is even louder than you expected! Even so, the harpy reacts rather slowly, taking a moment to finish her writing before even glancing in the direction of the noise. With a curious gait, she struts out of her desk and wanders off towards the aisle where it landed - finally leaving the book stand unattended! You quietly steal out from behind the pile and into the more open center space, shooting a glance at the harpy - from your position, she should have to come at you from the front to return the way she came.

You have a few precious seconds to plan your next move. You eye the glass case intently, and in mere moments you've assessed the situation. While at a glance the latch seems simple, you can tell that the lever has a magical lock overlaid onto it. With how elaborate that arcane lock mechanism is, it would probably be faster to use your-

THWAP!

Your vision goes blurry as you are knocked forwards by a blow to the head! The same book you threw earlier hits the ground next to you with a thud. You grip onto the desk just to keep your balance - but it isn't until a shadow looms over you that you realize who must have thrown the book at you...