Marc’s talking about the girls, of course. Buried inside every painting. Other than me, only he knows about their existence. The only thing I haven’t told him is why, fifteen years later, I continue to make them vanish over and over.
-- Narrator (Chapter 1)

Importance: Emma feels so guilty about what happened to Vivian, Natalie, and Allison that she keeps painting them and making them disappear, over and over. Marc knows the girls are hidden in the paintings, but he does not know why she hides the girls in the paintings.

I was the last person to see them alive. I could have stopped them from doing whatever the hell it was they had planned to do. Or I could have told Franny or a counselor as soon as they left. Instead, I went back to sleep. Now I still sometimes hear Vivian’s parting words in my dreams. / You’re too...
-- Narrator (Chapter 3)