Excellent, as I said, but actually not entirely standalone, because, like most of the recent episodes on Fringe, the individual story lines mirror what is going on in the deeper, continuing story. As we saw, and I cheered about, last week, Olivia is beginning to remember Peter.
There's much more of that tonight - Olivia basically remembers everything about her and Peter that we saw the first three years. My explanation for this is that Peter has returned to our world of the first three years (that's where he's been as soon he came out of the lake), bereft of memory of him at the start, but now, at least in Olivia, beginning to recall.
I pretty much still think that - though, based on what happened at the very end of tonight's episode, I'm not 100% sure. Walter thinks that Olivia, under the influence of cortexiphan, is super sensitive to Peter's thoughts and emotions. We did see Nina do something to Olivia a few episodes back - was it administer cortexiphan? Walter and Lee do find that some of it missing from its Massive Dynamic cold keeping. But ... Peter realizes that Olivia knows things from her past, relative to him, but that he didn't know until Olivia just told him. Ergo: Walter's theory that Olivia is picking up on Peter's thoughts can't be right.
Realizing this, Peter finally gives in and kisses Olivia - who promptly disappears (after walking into a gas station convenience store), and we see her held prisoner somewhere with Nina.
So, ok, good writing, I have no idea what's going on - I seriously like inscrutable stories - and we see in the coming attractions that we'll not only find out next week more of what's going on, but who the Eternal Bald Observers really are (bear in mind that September said Olivia will die in all possible timelines).
That's why I said that I'm no longer 100% sure that Peter is really in our first three years timeline now. But until I see a better explanation, I'm at least 96% percent sure.
... Fringe 4.2: Better and Worse Selves ... Fringe 4.3: Sanity and Son ... Fringe 4.4: Peter's Back, Ectoplasm, and McLuhan ... Fringe 4.5: Double Return ... Fringe 4.6: Time Slips ... Fringe 4.7: The Invisible Man ... Fringe 4.8: The Ramifications of Transformed Alternate Realities ... Fringe 4.9: Elizabeth ... Fringe 4.10: Deceit and Future Vision ... Fringe 4.11: Alternate Astrid ... Fringe 4.12: Double Westfield / Single Olivia