Gone.

“Elle, Lillie’s gone.” Before a silent tear crept its way down her face.
Part of me was missing... we were more like sisters not friends neither of us had siblings of our own and since infant school we had relied on each other, she was always at my side and now she was just... gone.

When Elle's best friend Lillie disappears she seems to leave no trace behind her but Elle knows her better than that.
She knows that she must have left something behind her.
And who is the new hot guy at school who seems just as interested in Lillie's disappearance as Elle?

Then Elle finds the list.