One summer day in 1897, a young singer, Enrico Caruso, arrives at the home of the Giachetti family. He has come to Livorno to sing on the summer stage with Ada Giachetti, a famous and beautiful soprano. Ada's mother offers him a spare room, and before Ada herself has a chance to meet the unknown tenor, her younger sister, Rina, arrives home from the market and falls fatefully in love.

With the help of singing lessons from Ada, Caruso wins the leading role in Puccini's new opera La Bohème. Although Caruso loves Rina, it is Ada he adores, and they soon become lovers. Heartbroken, Rina becomes an opera singer too, hoping to take her sister's place. For decades, the two sisters are locked in a struggle to be the star on Caruso's stage and in his bed, while Caruso's voice grows more and more unimaginably beautiful.

But as his relations with the two sisters break down in scandal and tragedy, the now world-famous Caruso builds a new life for himself as the star of the Metropolitan Opera in New York. There, far from the drama and passion of Caruso's Tuscan life, a shy young American woman will win his heart and, taking the greatest leap of faith of all, supplant Ada and Rina as his one true love.