The Secrets of the Cicada Summer — Andrea Beaty

Lily has read every Nancy Drew book in the library. She's great at spying clues and keeping secrets. She has to be. She has secrets of her own that no one can ever find out.

When summer brings lying, stealing Tinny Bridges to town, Lily must depend on her own wits to keep ahead of this sly newcomer. Tinny takes candy from the general store and blames Lily. She tries to steal Lily's friends and even her father's affection. Worst of all, she seems to know Lily's secret. When Tinny goes missing, only Lily has an idea what happened to her. But for Lily, finding Tinny means confronting her hidden past.