The Keeper of Secrets by Julie Thomas

Beautiful and mysterious, The Keeper of Secrets by Julie Thomas follows a priceless violin across generations—from WWII to Stalinist Russia to the gilded international concert halls of today—and reveals the loss, love, and secrets of the families who owned it.
 
In 1939 Berlin, 14-year-old Simon Horowitz’s world is stirred by his father's 1742 Guarneri del Gesu violin. When Nazis march across Europe and Simon is sent to Dachau, he finds unexpected kindness, and a chance to live.
 
In the present day, orchestra conductor Rafael Gomez finds himself inspired by Daniel Horowitz, a 14-year-old violin virtuoso who refuses to play. When Rafael learns that the boy's family once owned a precious violin believed to have been lost forever, Rafael seizes the power of history and discovers a family story like no other.