Not much to say here myself, except that it's weird seeing the, ah, weird sisters pop up at the start here, due to future events (not in this particular book, but in the series, so I'll take my own advice and not get all spoily-pants).
And wow, with this pathetic introduction to John Dee, it's fairly easy to feel all sorry for him and stuff! At least, until/unless you've read the rest of this particular story arc.