Sean Gallagher, a talented musician, leaves his remote fishing village in Ireland to find work in Chicago. But as circumstances conspire against him, he ends up busking on the streets, whereupon his violin is stolen, triggering an attack of epilepsy that lands him in hospital. Here he encounters Charles Peccatte, an imbalanced, pianist/composer with a brain tumor. What follows is an extraordinary meeting of minds - this culminating when Sean helps him to complete the final movement of a piano sonata.
Following Charles's death, Sean is compelled to find the rest of the sonata, a journey that leads him into the American south and to Marion Landray - while threatening to unlock a momentous episode from his own formative years.