Zero DayEnding, Explained: Who Was Responsible for the Cyberattack — and Is Proteus Real?

Mar. 15, 2025

(L to R) McKinley Belcher III as Carl Otieno, Mozhan Navabi as Melissa Kornblau, Robert De Niro as George Mullen, Jesse Plemons as Roger Carlson and Connie Britton as Valerie Whitesell in Zero Day.Photo:Courtesy of Netflix

(L to R) McKinley Belcher III as Carl Otieno, Mozhan Navabi as Melissa Kornblau, Robert De Niro as George Mullen, Jesse Plemons as Roger Carlson and Connie Britton as Valerie Whitesell in Zero Day.

Courtesy of Netflix

The season finale of Netflix’s new political thrillerZero Dayfinally reveals who is behind the nationwide cyberattack that took the lives of more than 3,400 Americans.

During the six-episode limited series, which debuted on Netflix on Feb. 20, the Zero Day Commission struggles to nail down who is to blame. Leads initially point to the Russians, but then George zeroes in on a domestic terrorist organization known as the Reapers. After the detainment and questioning of more than 40 U.S. citizens produce no solid leads and a second, smaller cyberattack on a consumer bank leaves the nation in turmoil, George appears to be losing control of the investigation — and the country is losing its faith in him. Worse, those closest to him, including his chief of staff Valerie Whitesell (Connie Britton), his top aide Roger Carlson (Jesse Plemons) and his wife Sheila (Joan Allen), are concerned the former president may not have the mental chops to see the inquiry through.

Also impeding the former president’s progress is Speaker of the House Richard Dreyer (Matthew Modine) and George’s own daughter, Rep. Alexandra Mullen (Lizzy Caplan), who opposed his involvement with the Commission from the onset. Dreyer makes Alex the head of the Zero Day Commission’s oversight committee, attempting to undermine her father’s work, and when the Commission’s headway stalls, Dreyer urges President Mitchell to get George to resign so he can take control.

As the final episode begins, the Zero Day Commission’s work appears to be complete. Kidder is believed to have launched thecyberattackas retaliation for the Federal Trade Commission’s investigation into her company for antitrust activity, and killed herself to avoid answering any questions about it. George, however, isn’t completely convinced. As he continues to pull at loose threads, he discovers that the individuals behind the Zero Day attack are not only within the country’s own government — but within his own home. He is left grappling with the choice to reveal the truth, or protect his own family.

Read ahead for theZero Dayending, explained — down to every last nail-biting moment.

Warning:Zero Dayspoilers ahead!

How doesZero Dayend?

Connie Britton as Valerie Whitesell and Robert De Niro as George Mullen in Episode 105 of Zero Day.

The sixth and final episode ofZero Daybegins with the apparent mastermind of the Zero Day attack, Kidder, dead in her prison cell of an apparent suicide. Speaker Dreyer is in his office, telling his media team to plant a quote in the news that places the blame for the attack squarely on Kidder, when Alex bursts in demanding answers. Their tense exchange reveals that while Kidder was responsible for deploying the malware that carried out the Zero Day attack, it was actually Dreyer, Alex and a group of congressmen and women who were the orchestrators of the plan. While Alex wants them to own up about their involvement, Dreyer insists that Kidder — and Kidder alone — needs to take the fall.

Alex leaves and phones her mother, who is at the family’s upstate New York home with George. She shares that she is on her way from D.C. to see them, and needs to talk to them both. Alex then issues an ominous warning to her parents (“Be careful”) as the second Zero Day attack hits — wiping out the power grid, cellular networks, FAA and mass transit. Unlike the first attack, though, this one is not just one minute long — it’s persistent.

During the blackout, Secret Service officers come to take George and Sheila to a safe house. But as they attempt to leave the Mullen family home, violent protestors attack their vehicle, pulling the protective officers into the mob and launching Molotov cocktails towards the former president and his wife. George and Sheila are saved when CIA director Jeremy Lasch (Bill Camp) appears out of the woods, dispersing the crowd with gunfire shot into the air. In the car, Lasch sends out a fake message on the long-range radio stating that George has been killed, before revealing to George that he andPresident Mitchellhave had reason to believe that the Zero Day attack came from inside the government. Now, they need George and the Zero Day Commission to confirm who.

As the country is still plunged in darkness and silence, George goes to work — first confronting his daughter Alex before arranging a private meeting with Dreyer. Alex confesses to her father, confirming that it was Dreyer’s plan and that their intent, as she understood, was just to scare people, not harm them. The goal, according to Alex, was to remind the country of how fragile and vulnerable it was, silence the extremists and conspiracy theorists in the aftermath and be able to move forward with positive change.

In the days leading up to his presentation of the Zero Day Commission’s findings before a joint session of Congress, George is left with an impossible dilemma: Expose the true perpetrators of the Zero Day attack and turn in his own daughter, or keep quiet about the government’s involvement and protect his family — and the country, who President Mitchell believes won’t survive a government conspiracy at this level.

Does George reveal who was truly behind the Zero Day attack?

Robert De Niro as George Mullen and Angela Bassett as President Mitchell in Episode 101 of Zero Day.Courtesy of Netflix

ZERO DAY. (L to R) Robert De Niro as George Mullen and Angela Bassett as President Mitchell in Episode 101 of Zero Day.

“This is what we’re going with,” George tells him definitively.

What does this revelation mean for George’s daughter, Rep. Alex Mullen and Speaker Richard Dreyer?

Matthew Modine as Richard Dreyer and Lizzy Caplan as Alexandra Mullen in Episode 103 of Zero Day.

Even before George exposed the truth about the Zero Day attack, Alex was prepared to turn herself in and accept the consequences. Though she did not attend her father’s speech, she left him a letter stating her intentions to come clean and writing how she planned to “confront hard truths, not hide from them.” George reads her letter out loud during his address, before pointing the finger at her co-conspirators.

As George concludes his congressional address, he implores President Mitchell to use every Constitutional power to bring justice upon the Zero Day traitors — including its ringleader, Dreyer. Dreyer, who was seated behind George as he exposed him, is furious and accuses George of destroying the country.

“Every time we can do the right thing, it’s another chance to save it,” George responds.

What about Proteus?

Jesse Plemons as Roger Carlson and Robert De Niro as George Mullen in Episode 102 of Zero Day.JOJO WHILDEN/Netflix

ZERO DAY. (L to R) Jesse Plemons as Roger Carlson and Robert De Niro as George Mullen in Episode 102 of Zero Day.

JOJO WHILDEN/Netflix

With George’s mental acuity in question, Sheila is subpoenaed to testify in front of the Zero Day Commission oversight committee. Dreyer asks Sheila directly about George’s state of mind, which she describes as “sound,” silencing any outside doubts about his decision making for the time being.

“Top-secret neurological weapon or just a tired old man with too many demons?” George wonders. “Does it really matter?”

Where does George go from here?

Robert De Niro as George Mullen in Episode 101 of Zero Day.

Will there be aZero Dayseason 2?

Robert De Niro as George Mullen in Episode 103 of Zero Day.JOJO WHILDEN/Netflix

ZERO DAY. Robert De Niro as George Mullen in Episode 103 of Zero Day.

source: people.com