One of the things that makes Fringe great is that the way the story has developed, minute character developments can be just as mindblowing as big reveals like the Twin Towers in the parallel universe. We watch Fauxlivia closely for any betrayal of her true identity. We watch, desperate for any character to show a glimmer of recognition that Fauxlivia is not Ourlivia. Part of the reason this storyline works in this show, when it has failed so completely in other shows, is that it is not completely obvious that it's the wrong Olivia. There are slight moments when she's a little 'off,' but that's it. We know it's not her, but we can't really fault any of the other characters for not knowing, owing to Anna Torv's fantastic parsing of the two Olivias.
We can't fault poor hapless Peter, who's obviously blinded by romance. We can't fault Walter, for obvious reasons. Astrid only ever dealt with Olivia on a professional level, so it's not surprising that she doesn't detect the nuances. But Nina. Oh Nina. She is the first to really cotton on that something's not right, which makes perfect sense. She and Olivia have always had an adversarial relationship, and so she has probably studied Olivia extensively to understand how to manipulate her. And Olivia has never been as forthcoming to Nina as Fauxlivia was in this episode, so that probably sent up some kind of flag. While it's slightly surprising that she didn't say anything during her heart-to-heart with Walter, we all know that Nina plays things close to the vest.
(Unless of course, as other commenters have suggested, there's a massive long con going on where Walter, Nina and Peter already know that it's the wrong Olivia, but that's too convoluted even for this show.)
THE ACTUAL EPISODE
The only way to get through the opening scene is to pretend it's Ourlivia, which makes it cute and fun, otherwise the whole thing is pretty squicky. But it is sweet, and mercifully short. I like that Fringe doesn't dwell too much on melodrama, instead using emotional moments for short and sweet effect, rather than using character drama as a substitute for a plot (cough cough LOST!)
There was a lot happening this episode (I am very grateful to Fringe that it advances the plot every episode, and doesn't treat it's mythology as the be-all and end-all of the entire show, unlike that other J.J. Abrams show). This episode gave us the first hints about how this particular storyline might resolve: Fauxlivia shows the first sign of hesitation about whether her mission is actually the righteous one. Between Nina, Walter and Peter, we learn about a key difference between Earth Prime and Alt-Earth: hope still exists in Earth One. Science can be used as a tool to help humanity, and not just for destruction. We get the sense throughout that Fauxlivia has only been exposed to science as a tool for military dominance, for keeping society in check, not as a constructive device in its own right. So when Peter tells her, Doctor-style, "There's got to be another way," you can see her almost start to believe it.
FauxLivia breaks cover on three separate occasions in this episode, each one not enough to blow it completely, but hopefully are sufficient to create a few scratches on her facade. The first is what I mentioned earlier, that she won't confront Walter directly, but asks Nina to do so instead. We all know Olivia is ridiculously brusque with Walter when he gets goopy (hence in Alt-Verse, all she has to do to prove that she's Ourlivia is yell at him, hilariously.) The next two are with silly Peter: first, she doesn't remember Ed Markham, midget bookseller extraordinaire. Then, more obviously, she betrays the fact that she doesn't have Olivia's photographic memory, when she struggles to recall the fateful numbers of Lost (sending me into shuddery flashbacks of hatred of Lost).
This episode also introduced an exciting new element: the First People, a race of humans that theoretically existed before even the dinosaurs. According to the only source, one Seamus Wiles, they were far more technologically advanced than modern man, and thusly proceeded to wipe themselves from the face of the universe. Also, most importantly, and I take absolutely no credit for noticing this, but ANAGRAM AHOY! Seamus Wiles = Samuel Weiss, who you will recall as being 'older than you think.' Before someone cracked that anagram, I assumed that the First People are one and the same as The Observers, but now I don't think so.
Finally, we get a tantalizing coda in the Alt-Verse, where we learn that Olivia is in imminent danger. And then I yelled at the tv for ending the episode. Cause shit be goin' down next week.
Walter and Nina, sitting on a bench, sharing a joint and lamenting 'kids these days.' It was a wonderfully warm scene with two characters we wouldn't normally associate with warmth.
Astrid actually has a role! And that role is channeling Alt-Strid and being a numbers whiz (seriously is there anything this girl isn't an expert in?) Sudden increase in screentime = red-shirt alert...