Since You've Been Gone/Morgan Matson

Emily's best friend Sloane disappears, almost without a trace - the only thing left behind is a to-do list. On it, thirteen Sloane-inspired tasks that wallflower Emily wouldn't normally do, and definitely not without her best friend. But what if completing the list could bring Sloane back? Dance Until Dawn? Sure. Why not? Kiss a stranger? Um ...Go skinny dipping? Wait ...what? Emily only has the summer to check everything off Sloane's list. The question is, what will she find at the end of it?