Leonard Nimoy will be back on “Fringe” this week, reprising his role as the mysterious William Bell.

Fox has released a couple of promo pictures from the episode that aren’t too SPOILER heavy.

They’ve also released a description of the highly anticipated episode.

Recuperating from the traumatic and alarming meeting with Massive Dynamic founder William Bell (guest star Nimoy), Agent Dunham consumes a powerful “fringe” concoction that Dr. Bishop prescribes to stimulate her memory. Meanwhile, the Fringe Division investigates a series of robbery cases in New York, Boston and Chicago that are tied to shape-shifting. As clues are tracked and memories are jogged, another woman experimented on by Dr. Bishop is introduced and a flashback reveals more about Olivia’s alternate-reality encounter in the “Momentum Deferred” episode of FRINGE airing Thursday, Oct. 8 (9:00-10:00 PM ET/PT) on FOX.

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