Sienna is unhappy. Her mother has disappeared and she feels alone in Shanghai. Her only friend is Rufus--a sarcastic invisible dog with a VERY clear idea of how things should be done.

When their mean housekeeper starts acting suspiciously, Sienna decides to investigate. She follows a trail of clues that leads her to a new friend, Feng, who also has an invisible animal friend and has lost a family member. Together they embark on a hunt through China that leads them to new friends, even more invisible animals, and a mysterious moonlit temple where Sienna's mother and Feng's brother were last seen.

Are the disappearances linked to a priceless statue of the famous moon princess? And can they discover the dangerous truth?