A Castle in the Clouds by Kerstin Gier
Way up in the Swiss mountains, there's an old grand hotel steeped in tradition and faded splendor. Once a year, when the famous New Year's Eve Ball takes place and guests from all over the world arrive, excitement returns to the vast hallways. Sophie, who works at the hotel as an intern, is busy making sure that everything goes according to plan. But unexpected problems keep arising, and some of the guests are not who they pretend to be. Very soon, Sophie finds herself right in the middle of a perilous adventure - and at risk of losing not only her job, but also her heart.