Stealing Magic (A Sixty-Eight Rooms Adventrue) by Marianne Malone

This is the second book in this series and just as good as the first book.  You don't need to have read the first book to understand what is happening, nor does this second installment cover the first book with too much description.  A great YA story for inventive imaginations.

Ruthie and Jack are smart and fun kids who have a good relationship with their parents and get drawn into the most wonderful mysteries. 

Ruthie and Jack thought that their adventures in the Thorne Rooms (the 68 miniature period rooms on permanent display in the Art Institute of Chicago) were over . . . until miniatures from the rooms start to disappear. Is it the work of the art thief who's on the loose in Chicago? Or has someone else discovered the secret of the Thorne Rooms' magic? Ruthie and Jack's quest to stop the thief takes them from modern day Chicago to 1937 Paris during the Nazi takeover and they get to visit the South when slavery was still in practice.

As more items disappear, including the key that allows them to shrink and access the past worlds, what was once just an adventure becomes a life and death race against the clock. Can Ruthie and Jack catch the thief and help the friends they meet on the way before the magic—and the rooms—are destroyed forever?