Opera?? in A&E's Nero Wolf - "Champagne for One," part I

[Naphtali]

I just received the complete Nero Wolf A&E series. Watching Disk One (first year's episodes), I have a question about background music in the mansion supper scene near the beginning of "Champagne for One," part I. Background music begins with Boccherini's "Quintet in E" and segues to possibly chamber music, possibly opera?? Regardless, the music and woman's voice singing it are beautiful. I know nothing about this kind of music; I'm hoping it is some form of opera because I'v envied those who appreciate it.

Anyone who can - please identify the music I've attempted to identify.