I looking to gain further knowledge about jazz music and theory in general. I currently listening to the "standards" in the Real Book to help get a better "feel" for what is jazz music, and how to play jazz. My question is the chord progression of the song Black Narcissus. It starts w/ Ab-7 , Bb-7/Ab, Ab-7, Bb-7/Ab and from that standpoint i understand the progression but then there is a change to F#-7, G#-7/F#,F#,G#-7/F#, and finally to AM7b5,FM7b5 and finally finish with CM7b5. And I'm looking for some help in understand the change in key(if in fact there was one), how and why it works. I still a relative novice to jazz but I'm listening intently and trying to get a better grasp. Any information is helpful.