The Secret Room (The Haunted Library, Bk. 5)

Kaz is an ordinary ghost. Sure, he can't glow or wail, and he can only just pass through walls without feeling all skizzy but he manages just fine. Then the wind separates Kaz from his family and carries him to a library far away, and he is scared he will be lost forever. That is, until he meet Claire - a human who can actually see him! Kaz and Claire must work together to find Kaz's family, while solving a few ghostly mysteries along the way . . .

Now that Kaz can finally pass through walls, he is excited to explore Beckett's secret room at the back of the library. In it he finds an envelope, some empty soda bottles, and a ghostly doll. Are any of these things connected? Kaz wants to return the doll to the ghost it belonged to, but that may be harder than he thinks.