Gal-chan started investigating the missing book at an old bookstore in the port town. As she explored the store with her child on her back, she found a lead. The book was a valuable historical document about the port town. Gal-chan decided to visit a historian to learn more. The historian was surprised by the book's disappearance. Gal-chan began to reason based on the information she obtained from the historian. Gal-chan thought about the secret room hidden within the book. Even the historian was unaware of its existence. Gal-chan was determined to find the room. Gal-chan successfully found the room. Inside, she discovered the hidden book and solved the case. However, another book she found in the room hinted at the beginning of a new case. Gal-chan steeled herself for the new challenge.
