As previous Fringe spoilers have revealed, multiple Observers are on the way.
In a recent interview with E! News, series star Lance Reddick previewed this, and one other, storyline on the way. He said:
"We've got a real page-turner of an episode coming up that's all about the Observers. And there's a whole episode about Broyles revisiting a case, a killer, that's the one that got away for Broyles. That episode introduces my ex-wife (Karen Holness) and talks about why we got divorced, and what my relationship with Fringe Division was in the past, versus what it is now."
This week's episode of Fringe is a major one: it will showcase Olivia's return trip to the alternate reality she visited in May.