Puzzle of the Paper Daughter — Kathryn Reiss

Julie discovers a mysterious note written in Chinese. She brings it to her friend Ivy to translate, and learns that the note once belonged to Ivy's grandmother, from long ago when she was a girl immigrating from China to San Francisco. The note promises great treasure, but it doesn't quite make sense--it's almost as if the writer was sending a secret message in code. Soon after the discovery of the note, Julie's and Ivy's beloved dolls are stolen. Who would do such a thing, and why? Seeking clues, Julie and Ivy search all over Chinatown and even visit the immigration station on Angel Island. Gradually, Julie realizes that in order to find the doll thief, she must figure out the real message hidden in the Chinese note.