The Ghost Backstage (Haunted Library)

Kaz and Claire's new detective agency is a success! Their latest case, though, is proving to be the hardest yet. When Claire's classmate says he saw a ghost backstage while rehearsing the school play, Kaz goes to school with Claire to investigate. From the description the boy gave, Kaz is sure it's his mom--but where has she gone? Kaz and Claire search everywhere and find no trace of her, but the mysterious ghostly activities are still happening...