But the deeper darkness of the show is the dark in Peter and Olivia's hearts over the loss of Etta, and the episode draws not only on Conrad's "Heart of Darkness," but Plato's "Meno" paradox, or a reversal of its axiom that that you can only know what you already know or have knowledge of, otherwise how could you know that you were really knowing anything?
Peter and Olivia each struggle with the darkness and their lack of knowledge in different ways. Olivia's new world is falling apart with her daughter gone, and Walter and she fear that she may lose Peter again. In the end, an unambered videotape of Etta as a little girl brings Olivia back.
Peter's path is a little different. The Observer's mocking him about his feelings for Etta pushes Peter to torture and kill the Observer - good - and also take the chip out the Observer's head and place it in Peter's. Is that also good? The tech reveal of the episode is that part of the Observers' superiority is indeed tech - ala Borg - in the brain. In this masterfully written episode by J. H. Wyman, not only philosophy reigns supreme, but The Matrix meets Star Trek.
What will the Observer tech due to Peter. Will he be able to absorb the Observer powers and retain his humanity? Will he be able to truly love Olivia, as he has up until now?
Fringe continues in its brooding brilliance towards finale.
... 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... Fringe 4.13: Tea and Telepathy ... Fringe 4.14: Palimpsest ... Fringe 4.15: I Knew It! ... Fringe 4.16: Walter Likes Yiddish ... Fringe 4.17: Second Chances ... Fringe 4.18: Broyled on Both Sides ... Future Fringe 4.19 ... Fringe 4.20: Bridge ... Fringe 4.21: Shocks ... Fringe Season 4 Finale: Death and Life