Chat Noir, while out on a patrol with Ladybug, finds a dairy. Not knowing who's it was, he takes out into the world to find who's it is. With no luck, he sits down to figure out what to do. Plagg convinces Adrien to read the dairy. Still not finding out who it belongs to, flips to the back of the page, hoping to find a name, but instead, finds the most important secret of them all. The dairy belongs to a girl named Marinette, who, according to the dairy, is Ladybug. Trying to give the dairy back without leaving a trace of him knowing her secret is hard work when something slips in desperate times. Pretty soon, all secrets between Adrien and Marinette come to the surface and Marinette/ Ladybug is surprised to find out who Chat Noir really is.