Nikki Maxwell's diary enters her bratty little sister's clutches in this sixteenth installment of the #1 New York Times bestselling Dork Diaries series!

It's almost time for school to start again, and Nikki is a little worried--but, as always, she has her BFFS to help. Only, it turns out her friends need Nikki's help. Nikki quickly gets overwhelmed and even starts feeling sick...which is when her little sister, Brianna, takes her chance to steal Nikki's diary! How much damage can Brianna do before Nikki is back on her feet?