A masquerade party quickly turns into a mystery when Nancy and Ned spy an enigmatic man in a black cloak and an exotic woman in a glittering Javanese costume.
Are they members of the gang of wily thieves who sneak into parties hosted by wealthy citizens to rob jewels and painting treasures?
Why is the owner of the black velvet hooded mask Ned found during the party desperate to retrieve it?
To find the answers, Nancy and George switch identities.
George soon discovers that it can be both exciting and dangerous to masquerade as Nancy Drew!