Oh, this is good, witty and poignant, as the best of Simon can be.  You write all the characters well, as usual.

Love the setting, and everyone's outfits.

I enjoyed imagining the crumb-spouting Peter and the elegantly aloof Snape.

Florence is so interesting.  Somehow I like the idea of an intelligent gal carrying a torch for that ingrate.  Somehow it's majorly intriguing.

And not that far out of canon if Harry is still a baby.  It would be sad if this Peter betrayed his friends though.

May you go to many more plays and may they give you ever more engaging and entertaining insitghts in to the Potterverse.