In my book, Broyles has been one of the criminally underdeveloped characters on "Fringe", and while this isn't the Broyles that we all know and respect from the Fringe Prime universe, it is a version thereof, and that's something!
It was a nice touch to link the case in this episode to Broyles' own son, tangentially to Peter's abduction all those years ago, and Olivia's attempt to maintain her cover while finding a way to get back to Fringe Prime. It's another great example of how they are managing to cover all the necessary bases while still progressing the story. (Especially since the ratings only improved marginally.)
This episode seems to bring the introductory phase of the season to a close, with Olivia's freedom now effectively gone and the truth about Fauxlivia about to be exposed. It's not quite how I thought it was going to happen, but it certainly means that the story is moving into a more complicated direction. Olivia's actions in this episode, particularly in terms of Broyles' son, will have to be a factor. Not only will Broyles' decision not to sanction Olivia bring consequences down on him, but it could play a role in her eventual survival (since it's unlikely they would kill her off!).
The actual reason for the abductions is interesting enough, and could intersect with some of what has been attempted in the Fringe Prime universe ("The Same Old Story"). This has been one of the interesting aspects of the dual-universe treatment: seeing how certain fringe technologies have evolved differently (or similarly). Of course, this has that Alt-Fringe twist on things: advanced technology and home chemistry kit coming together to create a chemical "fountain of youth".
Anna Torv did an amazing job in this episode. After all, she wasn't just playing an Olivia with doubts about her own identity. She was playing Olivia pretending to be Fauxlivia. Which, of course, she has been doing in reverse during the Fringe Prime episodes, where Fauxlivia has been posing as Olivia. This season has really shown Torv's range, and this episode is no exception.
But as good as the episode was, most of the attention has to go to the final few moments. Now that Peter knows the truth, it's going to be awfully interesting to see how it all plays out.