The combination of both Walter’s avoidance by burying himself into his work and Elizabeth’s unravelling also seem to be at the root of Peter’s anger towards Walter as expressed in Season 1, when one considers Peter’s comment to Elizabeth: “He makes you say that, doesn’t he” as a potential seed being sown. It only makes sense that, seeing, year and after year, Elizabeth’s suffering, and barely seeing Walter around the house, that Peter would have directed the bulk of his anger and displacement issues toward him.
And this is why we come back for more: because as oft mentioned, Fringe is a show about relationships. The ongoing, careful exploration of the various relationships that define the show adds new depths and layers to each character as well as to the overall plot. This episode particularly deepened the complexity of the character of Olivia, as well as her relationship with Walter. It also deepened the relationship of Walter with Polivia; after all, if Walter still remembers those tender moments between a young Peter and a young Olivia, it wouldn’t be much of a stretch to see why, on top of everything else, he has been the penultimate Polivia fan.
It does seem that the episode might only be about character development, as it doesn’t seem to add to the overall mythology. However, it is extremely satisfying for long time fans to see what they have been theorising about for so long. “Subject 13” was, typical of Fringe, about confirming what fans had mostly correctly guessed. However, there is the fact that in previous seasons, episodes such as this one which clarified theories of the past were composed of information vital for paving the way for the rest of the season. In a way, it’s as if, although before we could theorize, the Fringe production team knows that fans have to know the truth for the plot to continue. And just like with the Season 2 episode “Peter”, we had already guessed big parts of what happened in “Subject 13” and now are free to start theorising about other things.