The story follows Kaede, a young schoolteacher who frequently encounters small but puzzling mysteries in her daily life. Whenever she feels stuck, she turns to her grandfather, a former amateur detective who once belonged to a mystery club.
Although he is now elderly and affected by memory loss (dementia), he still has moments of sharp insight and impressive deductive skills. Together, they solve a series of seemingly simple cases—missing objects, strange incidents, and everyday puzzles that often hide deeper meanings.
As they investigate these mysteries, Kaede grows closer to her grandfather. Their collaboration becomes more than just problem-solving; it turns into a way of strengthening their bond while facing the emotional reality of his fading memory.