Gosick Episode 5: There's a Mysterious Ghost in the Abandoned Storehous

Kujo is still puzzling over Avril and cannot understand what is bothering him about her character. He begged Victorique to find him a book in hopes that it would give him a clue to Avril's mystery. Instead, Kujo is knocked unconscious and the book disappears. Victorique reveals to Kujo that the Avril Bradley he knows is actually an impostor and the successor of the legendary thief, Kuiaran. After Kujo rescues the real Avril Bradley, the duo confronts Kuiaran the Second on top of the library tower who came looking for the book.

Reference: http://en.wikipedia.org/wiki/Gosick