WARNING: The following contains spoilers for Season 1 of HBO's Run.

Fiona (Archie Panjabi) has been the thorn in Billy's (Domhnall Gleeson) side in HBO's Run, making it clear he won't crash his inspirational speaking career before she gets the payoff she deserves. It's why she's been tracking his running away with his university love Ruby (Merritt Wever), and why the personal assistant pretended to be a free-spirit called Alice to befriend the emotionally-distressed housewife.

Now, in the fourth episode, "Chase," it all comes to a head as Fiona drops the nice lady act and reveals her true hand to Ruby. And this time, she's willing to break both Ruby and Billy's lives to get everything she wanted, no matter the cost.

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Fiona's played Ruby for a fool with the Alice act, getting dirty insight into her family life that she can use as leverage. It's also to torture Billy who doesn't want her to let Ruby know the secrets of their self-help projects. There's something sinister Billy's hiding, even surrounding the pact he made to run away with Ruby. This is hinted with a video Fiona has with Billy speaking his followers detailing the pact suggesting there's something more to the eloping plan.

Eventually, though, Fiona gets fed up with Billy not giving her the payoff. She finds out from Ruby he's actually hoarding all his bank savings in their cabin on the train to New York and after ransacking it and not finding the loot, Fiona reveals her true identity to Ruby. Billy's out looking for his enemy, so Fiona has time in the cabin to play a recording she took of Billy and Ruby having sex in a Chicago hotel. She makes it clear she'll send it to Ruby's husband and family if Ruby doesn't give her the cash. Billy did ask his lover to keep the money in a bag, but now she has no choice.

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Ruby gives Fiona the loot and the businesswoman jets off, while also not deleting the sound byte as promised. Ruby's frazzled because apart from Fiona's sneaky ways, she also played on Ruby's insecurities, letting her know Billy hasn't revealed all the skeletons in his closet. However, when he gets back, he starts opening up to Ruby. At this point, she feels guilty and lets him know Fiona has the cash. He's upset and they start to chase her down because this is the money he wanted to use to start a new life with Ruby. Granted, they never spoke about a future officially and her leaving her family for good, but right now, Billy just needs the cash.

The episode concludes with a moment fit for Fast and Furious, Mission: Impossible or Liam Neeson movies, as Fiona gets to the end of the moving train. It's just pulled out of Chicago and isn't moving too fast, but it's not moving that slow either. Knowing she'll be arrested if she stays, Fiona jumps off and into the woods, leaving the couple wondering who the hell she really is. They're not going to do the same, well, at least maybe not until the next episode, but as pissed off as they are, Billy and Ruby are kind of impressed the lengths Fiona would go to. That said, she has Billy's nest egg and with Ruby's family not that interested in her anymore, she definitely sees merit in helping Billy get the cash back to embark on something together.

Starring Merritt Wever and Domhnall Gleeson, Run airs Sundays on April 12 on HBO at 10:30 p.m. ET/PT.

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