Time is running out on Timeless.

The sophomore season of NBC's time-travel drama wraps up with a two-hour finale on Sunday, and only ET has the exclusive sneak peek from the second hour -- yes, the actual finale episode! -- that sets the stage for an action-packed, whirlwind of a ride for the Time Team. Believe us when we say this: Your jaws will drop by the end of the season ender.

After Jessica's (Tonya Glanz) stunning revelation that she was pregnant and that Rittenhouse has surveillance photos of her, her loyalty has been called into serious question. Is she a sleeper agent for Rittenhouse? In Part 1 of the season closer, that question will be answered -- and as the sneak peek above reveals, it's not good news. Let's just say, she's not the same Jessica that Wyatt (Matt Lanter) married in his original timeline.

In ET's exclusive clip from Part 2 of the finale, the Time Team races back to the bunker seconds after Jessica has just abducted Jiya(Claudia Doumit) and taken the time machine with her to 1880s Chinatown in San Francisco. Wyatt, distraught over the unsettling truth that's just come out about his wife's true allegiances, makes a huge confession to the rest of the team about what he may have suspected about Jessica all this time.

"What did she do with Jiya?!" Rufus (Malcolm Barrett) yells out, frantically searching for the location of the missing lifeboat. "We asked you -- I asked you to tell us if she said or did anything to make you think she was Rittenhouse!"

Lucy (Abigail Spencer) defends Wyatt, not knowing that he had been hiding his own suspicions about his wife from the team. "He didn't do anything wrong. He didn't suspect anything," she says, trying to calm Rufus down.

"Her brother," Wyatt mentions. "In our original timeline, he died of leukemia when we were kids. But here, Jessica said that he had been saved by some stem cell therapy, which... I assume was not around in the 1980s."

"Why didn't you tell us?" Lucy pleads.

"Because I wanted to figure it out first. I told her she had to leave the bunker. I was trying to do the right thing. If your sister came back, would you assume she was your sister or would you assume she was some sort of a traitor?" Wyatt desperately asks. But when they look at him in dead silence, Wyatt knows they don't see eye to eye.

Earlier this week, ET spoke with Spencer about the response to the current season, which the 36-year-old actress admitted was both "wonderful and confusing."

"I feel how much people love the show and I feel such immediate feedback. Our reviews, the fan support, the acknowledgment of what we're trying to do intentionally with the show with underrepresented stories has been wonderful, and it's been an incredible platform for me personally being able to tell these women stories and tell minority stories and really wanting to commit social media or any way I can be a part of that change," Spencer said. "But the confusing part is that here we are with this incredible fanbase and our live viewership numbers are not great -- and it's so hard because we're still a network show. We're on the chopping block again. We don't know if we're going to get picked up. I feel so touched and grateful, and it's so amazing to have that immediacy of the interaction and for it to really be about something bigger than just entertainment."

The two-hour season finale of Timeless airs Sunday, May 13 at 9 p.m. ET/PT on NBC.

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