SPOILER WARNING: This article contains major spoilers for "Cause and XS," the latest episode of The Flash.
The Flash just revealed a key piece of information about Nora West-Allen's deal with Reverse-Flash. In "Cause and XS," the latest episode, Nora learned from her father that time travel has unintended consequences, often regardless of how normal everything appears. When Nora returned to 2049 to confront Eobard Thawne about it, he explicitly laid out the terms of their deal.
After Nora explained that she went back in time 52 times to save Team Flash from certain death, Barry shared one of the lessons he learned through his own time travel experiences using a mug as a metaphor. He cracked the mug so a piece fell off, then put it back together to show that it was whole again but didn't look the same. He compared this to time travel, explaining that the timeline had broken and couldn't be put back together again the same way.
Concerned, Nora fled to 2049 to confront Reverse-Flash. In an outburst, he told her he was the only speedster who truly understood time travel. He then revealed the terms of their deal: she would defeat Cicada and take his dagger, then they would save her father together.
Since the 100th episode, which aired before the "Elseworlds" crossover, the series has shown Nora work with Reverse-Flash several times. However, the nature of their partnership was largely unclear. Because of her father's absence, she turned to him for advice on how to be a speedster, but he otherwise kept mum about what he was getting out of the deal. Now, though, we know what he wants: Cicada's dagger. However, his plans for the dagger have yet to be revealed.
Airing Tuesdays at 8 p.m. ET/PT on The CW, The Flash stars Grant Gustin, Candice Patton, Carlos Valdes, Danielle Panabaker, Tom Cavanaugh, Jesse L. Martin, Danielle Nicolet, Hartley Sawyer and Jessica Parker Kennedy.