Walter had to drop some acid - that golden oldie expression - so he could eventually recall a password necessary to take the Boy Observer from his adoptive parents and put him to cause of beating the adult Observers who are still besetting and ruling our world. Peter thinks the Boy Observer comes from another timeline. Olivia says the Boy remembers her because Observers experience time in a different way from us. That may be true, but I still think we're currently in the original universe of Fringe Season 1, which Peter re-triggered when he came back into the show last year. See my reviews of last season for a more detailed explanation.
Anyway, the motif of the whole current season of Fringe has been to reinsert elements from earlier seasons, especially the first season. It's a pretty smart plot strategy, with lots of possibilities, because the first season characters here in the final season have repurposed significance that goes far beyond what they had the first time we encountered them. Clearly the Boy Observer will play some crucial role in our attempt to defeat the Observers. He'll fill in the gap in Peter's head and our mind power that was made last week, when Peter gave into love and removed the chip he had implanted in his brain.
Come to think of it, The Beatles "All You Need Is Love," was one of the high points of the psychedelic era, but also vacuous in comparison to the penetrating, mind-expanding lyrics of Sgt. Pepper. This was much like tonight's show, which as I said was at once high psychedelia with all the ruffles but really didn't advance the show more than a whisper or whisker or wisp of whiskey from where it was last week.
Love continues to be ascendant in this brief Age of Aquarius for Fringe. My favorite scene, though, was not psychedelic at all. Peter tells Olivia that he doesn't deserve her. She touches his face. All of this in a clearing in the woods with Observer skeletal corpses, with only the tattered remains of their clothing and their implants in view, withering on the ground. Is this the happy fate - happy for we 21st century humans - that awaits the Observers and us? Bones and implants on the ground for them, true love for us? Time - or the next month or so - will tell.
... 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