Netflix's Zero Day Ending Explained: Who Was Behind the Cyberattack? What Is Proteus?

Zero Day, Netflix's political conspiracy thriller, has a complex plot that's pretty confusing even if you're paying attention. The labyrinthine story follows a former president (played by Robert De Niro, in his first regular starring role in a television series) tasked with unmasking those behind a devastating cyberattack on the United States that sends panic among the populace, which was already unnerved by political division. (Sound familiar?) In the end, De Niro's George Mullen gets the answers he's looking for, but did the good guys actually win? Is America in a better position than it was before with the truth out? 

If you finished the limited series and still have questions, we'll do our best to answer them for you. We're your own personal former President George Mullen, on a fact-finding mission to unravel a vast conspiracy. 

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Who was behind the Zero Day conspiracy?

The cyberattack conspiracy was led by Speaker of the House Richard Dreyer (Matthew Modine). He was working with billionaires Monica Kidder (Gaby Hoffmann) and Robert Lyndon (Clark Gregg), as well as a dozen congresspeople and senators from both sides of the aisle, including Mullen's own daughter, Rep. Alexandra Mullen (Lizzy Caplan). Dreyer's goal was to, as he put it, "cut off the political fringe on both sides, to expose a vulnerability that has been mistaken for freedom, to restore a shaken faith in our ability to govern." 

The cyberattack was supposed to get the American people to unite in the face of a threat and give up their civil liberties in exchange for security and decisive governmental action. He wanted to be put in charge of the Zero Day commission, which would grant him sweeping powers and enable him to remake the government in his image on his way to becoming POTUS. 

But President Evelyn Mitchell (Angela Bassett) and CIA director Jeremy Lasch (Bill Camp) were suspicious of him, and Mitchell put Mullen in charge of the commission instead. Mullen uncovered the conspiracy, and ultimately decided to tell the American people the whole truth, in defiance of the President's wishes, and publicly named Dreyer, Alexandra, and the other conspirators. Mullen's actions might destroy the country, or they might restore faith in the government if people finally believe they're not being lied to. It's up to you, the viewer, to imagine what happens next. 

Who was Robert Lyndon?

Lyndon is a powerful hedge fund manager. It's not clear how Lyndon got involved in the Zero Day conspiracy, but his job is to know everything, so he found out somehow and got involved in order to profit from the chaos of the attack and manipulate the market toward his own ends. 

To do so, he leaned on Roger Carlson (Jesse Plemons), Mullen's right hand man, who he had for years been using for information and influence, through a combination of payment and blackmail. First he wanted Carlson to get Mullen to pin the attack on Russia, and when that didn't work out, he wanted him to neutralize cable news firebrand Evan Green (Dan Stevens), who had been talking about Lyndon appearing to have advance knowledge of the attack on his show. After Lyndon used his vast resources to vanish into thin air, Roger realized that he was directly involved in the attack. 

Who killed Roger Carlson and why? 

Two of the conspirators — Lyndon and tech CEO Kidder — were working together to try to control Roger. They sent a henchman to command him to get information exposing Mullen's mental issues, or else they would tell his semi-girlfriend Alexandra that he had hacked her phone. Rather than betray Mullen, Roger told Alexandra the truth, and when the conspirators found out that he wasn't cooperating, they killed him and made it look like he had relapsed on heroin and died in his bathtub. But they didn't know he had left Mullen a note implicating Lyndon, which in turn led them to Kidder when she sent her employee into a trap Mullen set at Roger's apartment.  

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How did Monica Kidder get involved in the conspiracy?

Kidder, a massively powerful tech billionaire in the style of Elon Musk, Mark Zuckerberg, and a few other people, was angry about the government's attempts to regulate her company, Panoply. She went to Dreyer with the idea for the cyberattack, which she would use to consolidate power and become the government's partner, not its adversary. She somehow got ahold of the NSA's malware design, modified it for her purposes, and deployed it through her company's apps, which were on 80% of the phones in America (don't get any ideas, Zuck). 

But when Mullen found out about her involvement, Dreyer cut her loose and pinned the whole thing on her. As he said, "she did do the things that she's accused of. The rest is becoming truth, and that's what matters." She was killed in her jail cell on Dreyer's orders, and her death was made to look like a suicide. That was supposed to be the end of it, with the public buying the story that she was the sole mastermind of the attack, but Mullen wasn't done pulling threads. 

How was Evan Green involved? 

Short answer is, he wasn't. Mullen hated Green for being a conspiracy theorist who fanned the flames of chaos and division, and targeted him for questioning based on false information fed to him by Lyndon. And while Green did interview people connected to the conspiracy, he was not personally involved. 

Green's sole motivation was personal enrichment. He didn't even believe the things he was saying, he was just giving his audience what they wanted so they would drive up his ratings and buy merch. He was a provocateur who used his influence irresponsibly. The character of Green is inspired by dishonest media figures – mostly ones on the right, judging by Green's visual and linguistic aesthetics, but some on the left, too.   

Was Mullen hallucinating because of Proteus? 

It's left ambiguous. Throughout the season, Mullen was having visual and auditory hallucinations and other symptoms of neurological illness, which may have been the result of the conspirators using a CIA-developed neuroweapon called Proteus on him. In the finale, Mullen found a piece of electronic equipment in a birdfeeder on his property, and passed it along for forensic analysis. 

The test results came back inconclusive. His chief of staff Valerie Whitesell (Connie Britton) called it "debris of indeterminate origin" that could have been part of a transmitter attached to the feeder, or could have been junk that fell into the birdseed at the packaging plant. She said that the doctors think Mullen's symptoms could have been caused by stress. 

"Top-secret neurological weapon or tired old man with too many demons?" Mullen said. "Does it really matter?" So it could be either. The show doesn't answer one way or the other. It's an intentional loose end.

Why did Mullen throw his memoir in the fire? 

In the final moments of the show, Mullen throws the manuscript of the memoir he's been struggling to write into the fireplace in his home office. He's alone when he does it, so he doesn't explain himself, which means his action is up to interpretation. 

The most likely explanation is that the memoir, which he started before Zero Day, was not the truth. It didn't reveal the whole reason why he didn't seek a second term, which wasn't just that he was grieving the death of his son, it was also that he had fathered a child with Valerie and it would be easier to protect the child if he wasn't President. Mullen believes in truth for truth's sake, as his exposure of the Zero Day conspiracy shows, and he wouldn't be able to publish something that wasn't the whole truth. 

Whether he starts over and writes an honest memoir or somewhat hypocritically holds onto the truth for the sake of his family is another thing that's up to the viewer to imagine and debate what the right thing to do is. 

Zero Day is now streaming on Netflix.