Dominique is suspicious of rich Uncle Brazzi's charm; he's a bit too friendly with her when they first meet. As the film/story progresses, they become more attracted to each other, and they eventually fall in love. Or so she thinks... Poor Joan. As the stressed-out wife, she's only a supporting player in this, but she has some very good scenes, especially when she confronts Dominique about the affair, and teaches the young girl a thing or two, which is I think is the best scene in the film. Dillman also has a good scene when he finds out; it's a good drunk scene.
One thing I noticed is that in almost every scene she's in, Joan's character is chugging a cigarette. I highly doubt Ms Fontaine was a serious smoker offscreen, otherwise I don't think she would have lived as long as she has. Though she did appear in those Chesterfield ads.
Ms. Carère's accent is a bit thick, and I had some trouble making out what she was saying much of the time. But she is very talented and I wish she would have made more films; she was only in a few American films before she retired from acting in the 1960s. Other than that, I don't know anything else about her. Unfortunately her name is not one that most other people will remember either. However, you might not be able to forget her once you see A Certain Smile.
The theme was a big hit song, made famous by Johnny Mathis.\