The book "Thirteen Plus One" came out in 2010.
lars finds out he's adopted, and that he can no longer be around winnie because she's only 14
Two plus eleven = thirteen.
The tenth would be before the thirteen plus one if my logic is the logic you want.
The climax of the book Thirteen by Lauren Myracle is when Winnie's mother gets pregnant with a girl and Winnie has a new baby sister.
the theme is having a boyfriend
Eleven and Twelve: Trinity Twelve, Thirteen, Thirteen Plus One: Westminster
Nine plus four equals thirteen and that's ONE baker's dozen.