Marie-Laure sits in her laboratory at the Natural History Museum, thinking of Werner. She realizes that after she and Werner parted ways in 1944, Werner must have gone back to open the gate to the grotto and find the model house. Marie-Laure takes her model house and twists it open. Inside, she finds an iron key.
Here part of the mystery is revealed—Werner did indeed return to the grotto and find the diamond, but then he made the same choice Marie-Laure did, and left it there. Neither protagonist allowed themselves to be seduced by the glamour or value of the diamond, but simply treated it as another object with symbolic value—an object only useful to them as an aspect of human connection, like a radio or a model house. This also symbolizes both characters casting away the influence of fate (the diamond’s curse) and trying to take their destiny into their own hands.