The chapter title refers to a proverbial box that Ai opens when she asks about the relationship with Yuki, Zero, and Kaname.
While Kaname Kuran is walking in the woods at night, an elderly vampire tells him that he shouldn't be there. Ren Kiryu and Ai Kuran arrive, and Ai sends the woman on her way. There's a wound on Ren's cheek from a branch, but Ren wipes the blood away and it's already healed. Musing about a vampire's healing ability, Kaname asks if the woman inside him would regenerate if they pulled her out of him. Ai asks if he wants to try, but Kaname thinks the woman inside him would be very angry.
Ai recalls pulling a lid off a box that she shouldn't have, and she remembers Yuki brushing her hair. All made up, Ai comes out and Zero sees her dress. She's going to her first soiree. At the event, Ai gets defensive and punches those who ask her to dance because she doesn't want to be touched. When they get back, Zero asks about them returning early, and Ai bursts into tears and hugs him, and comments that she doesn't mind when it's Zero holding her.
Zero leaves for the night, and Ai asks her mother about him no longer staying over. Yuki explains that they decided it's best for now. Ai opens the lid on the proverbial box by asking if Zero is angry because Yuki still loves Kaname. Yuki explains a little, saying that Zero and Ai rescued her from the darkness of losing Kaname, which is how Ai first began to learn about the history of the three of them.
Characters in order of appearance: