The Five O'Clock Ghost #4 (The Haunted Library);

Kaz and Claire are back for a timely mystery in this adorable series by Edgar Award winner Dori Hillestad Butler!
 Kaz and Claire are called in for another ghostly mystery, and this ghost is always right on time. When Claire's friend tells the young detectives about his five o'clock ghost, Kaz wonders if it could be his own missing brother, Little John. Kaz and Claire search the house up and down, but they can't find any trace of Little John--or any other ghost. Yet when five o'clock comes along, the strange occurrences come back again...