A Mysterious Note is located in an upper room of the Legerdemain Lounge in Dalaran in the Broken Isles.
This item is an objective of  Message from the Shadows.
Preparations are nearly complete. As we speak, our bretheren scour the shadow markets of the Underbelly to acquire the final reagents for the ritual.
Everything will be ready for the appointed day.
Shadows light the way,