I've seen some of Fringe, bits and pieces from different seasons (and I can't place where and when). I know about the other universe/world, I've seen the observers, but I don't know how relvant that is to season 5. It starts on the 24th of October in the UK and I'd like to catch up.
Which episodes seem most vital to understanding whatever story season 4 left hanging for season 5 to pick up? Or has it started afresh?
4x19, Letters of Transit, is very important, considering Season 5 is a direct sequel, but there is something even more important:
In the middle of 4x14, The End of All Things, Peter goes into September's mind and gets some extra information about the timeline. Given the lengths the Observers have gone to in correcting September's mistake in 1985, and the.. strangeness.. about Etta, I have the feeling that this information will become important later on.
The finale, Brave New World parts one and two explain Walter's anger at William Bell during the events of Letters of Transit. They also contain an explanation for a blink-and-you'll-miss-it scene from 5x01 that otherwise looks like a small Deus ex Machina.
Then there's this quote from the Comic-Con trailer for Season 5:
Peter: "We need to keep those bald-headed bastards occupied."
Olivia: "What'd you have in mind?"
Peter: "I think it's time we caused a few Fringe events of our own."
Throughout the trailer are montages of various Fringe events throughout the series. The implication, as I understand it, is that they're going to take Fringe events from previous seasons and bring them to the next level - just like they did with Amber between its introduction in Season 1 and its usage to seal vortexes in later seasons.
I'm not saying you should make sure you've seen the entire series (Yes, I am), but I get the feeling that having at least an idea of what's happened in previous episodes will make Season 5 easier to understand, similar to how knowing Season 1 has given a lot more insight into events in Season 4.
This said, I do overall agree that it'll be hard to know what else is necessary until more of Season 5 has aired: Just look at what I've mentioned so far - I would not have thought of half it except that I've already seen 5x01.
If your really want to take a huge shortcut, it's imperative that you see Letters Of Transit, the 19th episode of the fourth season.
The first episode of season 5 is a direct continuation of this episode, and as I noted here, it drops must plots point that where currently going to transport the story in 2036.
I think it's too soon state anything for the rest, as we don't know if the story will stay on this route or come back where season 4 ended.
