In a total departure from her usual fare of FBI profilers, Gerritsen takes the reader on a journey that starts in WWII Italy to present day Boston where Julia Ansdell lives with her husband and daughter. While in Rome, Julia, a professional violinist, purchases a book of gypsy sheet music for her collection. Tucked inside the pages is a single sheet of hand written music, a waltz. Julia is immediately intrigued by the passion and complexity of the music. Upon returning to Boston, Julia sets out to master the haunting and difficult piece, titled Incendio, setting into motion something strange and mysterious which threatens the safety of Julia and her family.
In Venice, before WWII, music is a huge part of young Lorenzo Todesco's life. His grandfather Alberto is a violinist and music professor at a local university, his father Bruno a skilled craftsman of violins, and Lorenzo is a gifted violinist. When his grandfather mentions the possibility of Lorenzo teaming up with his colleague's daughter Laura, who studies cello, they enter a duet competition at the university. Lorenzo and Laura practice for hours and, of course, fall in love. At first with the music they make together and then with each other. Laura and Lorenzo have barely acknowledged their feelings for each other when the war separates them. Lorenzo clings to music and his memories of Laura as the Nazi troops sweep the Jews from Italy. From his ring side seat he composes a tribute to his love for Laura.
The danger threatening Julia's family takes her back to Italy and Venice to search for the origins of Incendio and it's composer. The closer Julia comes to discovering the story behind the waltz the more danger she is in. Someone needs to keep the story from being told and the music from being heard. Meanwhile, Julia's life back home in Boston is falling apart. As her husband and her sister struggle to understand Julia's obsession and preoccupation with the waltz they worry about the affect the waltz is having on the family.
With her family in danger, Julia has no way of knowing if uncovering the truth of the waltz will save her. In Playing with Fire Gerritsen has composed a dark and compelling thriller.