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Book 1: The Haunted Library
This is a story about a ghost boy who finds himself in a new, unknown place for the first time in his life - a library full of people. It's very strange to see so many people in a room, and even stranger when one girl sees you for sure and wants to be your friend. And despite their differences, they are united by a desire to solve mysteries.

The first "criminal case" was not long in coming: Claire's grandmother tells them that a ghost has been living in the library for a long time. Will the friends be able to neutralise the unfriendly ghost? The Ghost Under the Roof
Having lost her parents, Kaz finds herself in a library house where an unusual girl Claire lives. She can see ghosts and communicate with them. The last adventure to find a mysterious ghost in the library brought Kaz and Claire together, so the children decided to create their own detective agency to find ghosts. Maybe this will help them find Kaz's family.