The Thief - Hope Chest Series, #4

On the run from a failed attempt to steal back his family's historic treasure, the thief known only as Delgatto stumbles into the ruins of the Chesterfield Hotel and finds an old wooden chest. When he touches the gold chain inside, he's hurtled back well over a hundred years to the Chesterfield, during its days as a bustling resort filled with wealthy patrons.  He meets the enigmatic Miss Sparrow who arranges for him to "borrow" the identity of a rich French count.
That's when he realizes he's in the exact time and place where his family's missing treasure, the priceless emerald known as "The Heart of Saharanpur", was last seen. However, when he spies the legendary gem around the neck of a green-eyed beauty at the Christmas Costume Ball, he's not sure which treasure he wants more-the emerald or the masked beauty wearing it. Trouble is, he has no idea who she is.
A wealthy widow? An affluent ingénue? A moneyed mademoiselle? Or perhaps a green-eyed maid named Emily Drewett, who was offered a one-time chance to forget being a maid for one day in order to play Cinderella? Originally published as Stolen Hearts.