La ninfa constante (1943)

Lewis Dodd (Charles Boyer) is a Brussels-based modern composer. His latest symphony, which just premiered at the Regent Theatre in London, is an unmitigated flop, deemed to be too mechanical. He considers the more melodic piece he wrote for his friends, the Sangers, to be trifle. The Sangers, a poor family of musicians, are his dearest friends, they who live in a mountain chalet nestled within the Swiss Alps. Patriarch Albert Sanger (Montagu Love) believes Lewis has a real talent for melody writing, which is against the mathematical way of composing his modern pieces, and encourages him to expand that so-called trifle into a symphonic poem. One of Sanger's daughters, teen-aged Tessa Sanger (Joan Fontaine), has heart problems, which are exacerbated more by emotional distress than physical exertion. Tessa is just at the age where she is beginning to have womanly feelings. Her life-long affection for Lewis has now turned into romantic love, of which Lewis is unaware. Instead, Lewis falls in love with Tessa's London-based first cousin, the wealthy and sophisticated Florence Creighton (Alexis Smith), who, along with her father Charles Creighton (Charles Coburn), have come to Switzerland to look after their poor relations following Albert's death. They marry. But Lewis and Florence immediately begin to have problems in their marriage, which are compounded by Lewis doting on all the Sangers --- the special bond he and especially Tessa seem to have most specifically about his music --- and Florence not being oblivious to the fact of Tessa's love for her husband. The question becomes how this romantic triangle will play out.