It's time to accept that Whiterose and her Dark Army — not E Corp — are the true villains of Mr. Robot. Spoilers for the Nov. 22 episode follow. The Dark Army killed Trenton and Mobley on Mr. Robot in "Eps3.6fredrick&tanya.chk" after the Chinese hacker organization enacted their own version of stage two. The two fsociety members had fled New York City and were last seen in the Season 2 finale, "Eps2.9pyth0n-pt2.p7z." But despite trying to start new lives for themselves, their involvement in fsociety had deadly consequences, just as they had anticipated.
In Season 2, Trenton and Mobley left New York City after Darlene killed E Corp attorney Susan Jacobs. They had started new, albeit lackluster, lives in the Southwest working as Fredrick and Tanya at an electronics store. However, Dark Army soldier Leon approached Trenton and Mobley in the very last moment of Season 2, so you should have assumed things would not end well for this pair. After all, Leon didn't ask about the time — Whiterose's favorite topic — by accident. And even though it's not Leon who actually pulls the trigger on the two of them in "Eps3.6fredrick&tanya.chk," Whiterose and her Dark Army are responsible for their deaths.
Trenton and Mobley's murders are coldhearted, but they serve a purpose. Before they kill Elliot and Darlene's compatriots, the Dark Army frame the two hackers to make it look like they were planning a terrorist attack with airplanes. The Dark Army is pinning the explosions of the E Corp buildings on fsociety, which is laughable considering the only members of the hacker group alive now are the Alderson siblings. Yet, the Dark Army has been steadily establishing this cover.
In the fourth episode of Season 3, an intentionally captured Dark Army member lied to Dom at the FBI and said that he was an fsociety follower. Just like most of the FBI (excluding double agent Santiago) thinks that Tyrell was the mastermind of stage two, they think fsociety is the organization behind all of the destruction and chaos — and that another attack by Trenton and Mobley was just avoided. But in the wings, Whiterose and her Dark Army are really the ones pulling the strings.
Trenton and Mobley's fate proves that the Dark Army are completely ruthless when it comes to their master plan. And their deaths serve as a reminder that Elliot, Darlene, and Angela are in way over their heads when it comes to the Dark Army — particularly, Angela. During "Eps3.6fredrick&tanya.chk," Whiterose, as Minister Zhi Zhang, reveals to Price that he targeted Angela to stop her from investigating the Washington Township power plant. After their meeting, Angela believed that Whiterose had the ability to change time. That could still be true, especially when you consider that Trenton said in the Season 2 finale, "We could potentially undo this whole thing, put everything back the way it was." But after the attacks on the E Corp buildings, Angela's faith in Whiterose is broken — and as a result, she's broken too.
Darlene sees firsthand how Whiterose destroyed Angela when Angela tries to convince herself with the DVR that the innocent people who were killed in the E Corp explosions survived. Although Darlene doesn't completely understand what's happening, she can assume that her childhood friend was massively manipulated to end up like this. And with Elliot flipping back and forth between his own identity and Mr. Robot, Darlene is the group's best hope to put the pieces together. She also has a line of communication with Dom and while Dom seemed more like a savvy nuisance than anything else in Season 2, it's now looking like she will be invaluable when it comes to stopping the Dark Army.
Dom is the only FBI agent to seem suspicious about the way that Trenton and Mobley died. And because of that, she may approach Darlene about their deaths, knowing that they were connected through fsociety. Darlene will probably be devastated that her friends have died, but she'll also be astounded to hear that Trenton and Mobley, who didn't want anything to do with fsociety in Season 2, were allegedly planning an attack. Darlene will know that someone was setting them up — and the one group who has the power to do that would be the Dark Army.
The deaths of Trenton and Mobley may push Darlene to genuinely cooperate with Dom to take down the Dark Army. And at this point, the combo of Darlene and Dom seems like the last hope to stop Whiterose from doing whatever the hell it is that she is doing. So while you are right to mourn Trenton and Mobley, perhaps something good can come of their brutal murders.