The new show on Netflix called Zero Day depicts the aftermath of a frightening cyber assault on the United States. The term “Zero Day” refers to a specific day when all electronic devices, including phones and computers, as well as electricity, cease to function simultaneously, posing a significant threat to American security. The central question in the series revolves around the identity of the mastermind behind Zero Day, a mystery that retired President George Mullen (played by Robert De Niro) is determined to unravel.

As President Mullen dives deeper into the mystery, it’s clear there’s a terrifying conspiracy at the heart of Zero Day that includes everyone from Russians and hackers to shady billionaires and tech moguls. How does Netflix’s Zero Day end? Who did Zero Day?

**Spoilers for all six episodes of Zero Day, now streaming on Netflix**

Over the course of Zero Day‘s six episodes, President Mullen and his Zero Day Commission find evidence linking Zero Day to all sorts of people, from a hacker named Patrick O’Keefe (Jasjit Williams) to the smug, plaid-shirted, political talk show host Evan Green (Dan Stevens).

Adding to the suspense is the fact that George Mullen himself might be a risk to the country. On the surface, he appears to be hiding the fact that he’s suffering from cognitive decline. He’s haunted by the song “Who Killed Bambi?” and forgetting key details from his own life. As the investigation into Zero Day heats up, George indulges his own worst instincts, letting his team threaten and torture civilians during interrogation.

Ultimately, George Mullen is absolved of all this because it turns out that he neither has dementia and he’s able to identify the real perpetrators of Zero Day.

So how does Zero Day end? And who is responsible for Zero Day? Here’s what you need to know about the end of Zero Day on Netflix…

Zero Day Ending Explained: Who Was Behind Zero Day?

So who was responsible for the cyber attack in Netflix’s Zero Day? Well, it turns out it was a shadowy cabal of billionaires and politicians, including President Mullen’s own daughter Alex (Lizzy Caplan). Dun-dun-DUN!!!

We learn in Zero Day Episode 6 that Republican Representative Richard Dreyer (Matthew Modine) has worked in secret to organize a coalition of congresspeople from both sides of the aisle. To pass legislation that would help the American people? Heck no. Instead, this group worked with rich creep Robert Lyndon (Clark Gregg) and the Elon Musk-esque Monica Kidder (Gaby Hoffman) to do Zero Day.

Lyndon benefited from Zero Day because he was able to short various stocks in the lead up to the event. Kidder perfected the technology and used her sprawling tech empire to seed the cyber attack. The politicians? Well, the idea was that Dreyer would lead the Zero Day Commission and use that power to squelch extremists on both sides of the aisle. Then, congress could work to fix the country.

“I think there was great truth to to what he was saying,” Zero Day star Matthew Modine told Decider. “It was the methodology, do you destroy something in order to fix it, or do you find a way to work together with your political opponents to be able to find a workable solution that doesn’t cause the death of thousands of people?”

Lizzy Caplan also said she hoped the scene where Alex confesses why she’s done this to her father “does make some sense” to viewers. “Like not that anybody would necessarily recommend doing what she did, but that maybe it could start to make a little bit more sense why she made those decisions,” Caplan said.

While Alex insisted that she had no idea anyone would die on Zero Day, Modine scoffed at the idea that Dreyer was clueless about the destruction he was plotting.

“I know that when I go out on the street and the traffic light turns red, that the cars are going to stop and it makes it safe for me to make a crossing, to be able to get across the street without being killed,” Modine said. “So somebody who who willfully does something like that knows that you’re going to create instability and chaos across the country.”

It’s not enough that George Mullen figures this out, though. He has to figure out what to do with this information. Because Zero Day Episode 5 ends with Kidder not only apprehended, but also found dead in her cell, Epstein-style, there’s good reason to use her and the off-the-grid Lyndon as the scapegoats. The reasoning posed by President Evelyn Mitchell (Angela Bassett) is that Americans’ faith in the government will completely erode if they know Dreyer, Alex, et al were also complicit.

George initially goes with the plan to hide the politicians’ involvement, publishing a report singling out Lyndon and Kidder. However, when he publicly reveals his findings, he pulls out a letter that Alex has left for him. In it, she admits to her crimes. This allows Mullen to also name Dreyer and the other Zero Day conspirators.

“I kind of like the letter,” Caplan said. “I think it’s a subtle and and a cool way to do [the reveal]. And he has to make a really difficult choice, to protect his family or does he do the right thing?”

Zero Day ends with the truth being revealed and George returning to his normal retired life, contemplating whatever it is former Presidents contemplate.

“The series ends with George Mullen obviously making a pretty dramatic decision with wide ranging consequences,” Zero Day executive producer Noah Oppenheim said, before admitting that the door could be open to see what happens next. “You know, we every now and then chat about what might what could happen.”

What’s Wrong With Robert De Niro’s George Mullen in Zero Day: Dementia or Proteus?

Another mystery plaguing George Mullen in Zero Day has to do with his own grip on reality. The former President is clearly experiencing memory loss and hallucinations. The obvious answer is he is suffering from a form of dementia, but Zero Day offers another explanation: a weapon called Proteus.

Zero Day Episode 5 essentially explains that some outside force is targeting George with a neurological weapon called Proteus, which is why he keeps hearing “Who Killed Bambi?” at tense moments. However, Episode 6 leaves it nebulous.

“When Noah and I were writing it, we made a decision that it was happening. That there was some kind of sonic microwave technology that was being used against him,” executive producer Eric Newman said. “Whether we would confirm it or not in the show was undecided, but just for our purposes, we had sort of agreed yes, it’s happening.”

George does not have dementia. In fact, he is a victim of Proteus.