"Agents of S.H.I.E.L.D.'s" fan-favorite couple just landed in a world of trouble. In "The Man Behind the Shield," last night's episode, Leo Fitz and Jemma Simmons came to the horrifying realization that some of their friends had been replaced with Life Model Decoys like Aida. Now, the two scientists will have to race to save S.H.I.E.L.D. from these LMDs -- and it could very well cost them their lives.

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A new ad for the "Self Control," next week's episode, hints that this operation could be FitzSimmons' last. With the tagline "Together Until The(ir) End?", it suggests that one -- or even both -- of them could die as a result of this infiltration.

Fitz and Simmons will face LMD versions of their friends in Self Control.

"Man Behind the Shield" found Coulson, Daisy, Mack, Fitz and Simmons tracking the Superior to a Russian base. Once inside, the team split up. Coulson and Daisy fought the Superior, while Fitz tried to glean information off of the base's computers and Simmons tried to track down Aida after another agent spotted her. Meanwhile, Mack went and recovered Jeffrey Mace, who was brutally attacked by a handful of Watchdogs. However, during this time, each of the team members were separated for a good length of time -- and it was just long enough for some (or all) of them to get replaced by LMDs.

Unfortunately, Fitz and Simmons didn't realize this until they were back on base. There, Simmons received a notification that the LMD detection device at the base's entrance had been turned off by none other than Phil Coulson. When Fitz and Simmons looked closer, they saw that it had been turned off for a brief amount of time, during which Mack, Daisy, Coulson and Mace passed through the detector. That's when it hit home for them: there were rogue LMD versions of their friends on base.

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To make matters worse, the end of the episode saw Coulson resurrecting the May LMD. As such, it's clear that -- at the very least -- Coulson has been replaced. As of the conclusion of "Man Behind the Shield," though, none of the other characters have been confirmed as LMDs.  As such, Fitz and Simmons will have their work cut out for them in "Self Control" -- if they make it that long.

Airing Tuesdays at 10 pm ET/PT on ABC, “Marvel’s Agents of S.H.I.E.L.D.” stars Clark Gregg as Agent Phil Coulson, Chloe Bennet as Daisy “Quake” Johnson, Ming-Na Wen as Melinda May, Iain De Caestecker as Leo Fitz, Elizabeth Henstridge as Jemma Simmons, Henry Simmons as Alphonso “Mack” Mackenzie and more.