The Homemade God by Rachel Joyce

There is a heatwave across Europe, and Goose and his three sisters gather at the family's house by Lake Orta in Piedmont, Italy. Their father, a famous artist, recently remarried a much younger woman and decamped to Italy to finish his masterpiece. Now he is dead. And there is no sign of his new wife and or his final painting. Though the siblings have always been close, the things they learn that summer - about themselves, their father and their new stepmother - will drive them apart before they can come to any kind of understanding of what their father's legacy truly is.