Zero Day Ending Explained: Who was Behind the Cyberattack & What Happened to President Mullen?

Netflix’s political thriller Zero Day captivates viewers with its tense plot, led by Robert De Niro as George Mullen, a former U.S. president thrust back into the spotlight following a massive cyberattack. The attack sends the country into chaos for one full minute, causing catastrophic consequences. Thousands of lives are lost, and the government is on high alert, trying to prevent a second wave. 

As Mullen works to uncover the truth, he faces personal battles with his mental health, his past, and a deeply entrenched conspiracy. In the end, the truth behind the attack—and Mullen’s role in exposing it—unravels in a shocking twist.

The Cyberattack and the Search for Answers

The show opens with Mullen, now a retired figure, preparing to complete his memoir, only to be pulled back into public life after the attack. The cyberstrike, which briefly disables the nation’s power grid, cripples essential systems, including trains, planes, and medical equipment, resulting in widespread fatalities and chaos. The government initially suspects foreign powers, with Russia as the primary target. 

However, Mullen’s investigation reveals a much darker truth: the attack is not an external threat, but a domestic one orchestrated by a radical left-wing group known as the Reapers. As Mullen digs deeper, he grapples with his own deteriorating mental state, experiencing forgetfulness and hallucinations.

His condition casts doubt on his ability to lead the investigation, and soon, he’s using unchecked power to crack down on suspected members of the Reapers. However, Mullen’s ethical boundaries are tested as he spirals into paranoia, leading him to abandon due process.

The Proteus Mystery and the Mind Games

A key subplot involves Mullen's suspicions that his mental deterioration is the result of Proteus, a secret government program designed to manipulate individuals neurologically. Believing that the cyberattack’s perpetrators may be using Proteus to undermine him, Mullen investigates further. 

However, the show leaves ambiguity about whether Proteus is real or just a figment of Mullen’s troubled mind. In the end, the device he suspects to be linked to Proteus is found in his birdfeeder, but it proves to be irrelevant to the mystery. This ambiguity fuels the larger theme of uncertainty, both in Mullen’s mind and in the broader political world.

The Real Culprits

As Mullen’s investigation unfolds, the true architects of the cyberattack emerge: tech billionaires Monica Kidder and Robert Lyndon, along with a network of government officials, including Mullen’s own daughter, Congresswoman Alexandra Mullen (Lizzy Caplan). 

Kidder’s involvement is revealed when it’s discovered that she had perfected the technology used to disrupt the nation’s systems. Despite her attempts to bargain for immunity, Kidder ends up dead under suspicious circumstances, leaving many questions unanswered.

In a shocking twist, it is revealed that several high-ranking members of Congress—including Alexandra Mullen—were part of the conspiracy, aiming to use the attack to push a radical shift in government. Their motives were driven by a desire to ‘reset’ the country’s trajectory, believing that such an extreme measure was necessary to restore order.

The Shocking Finale: Truth and Consequences

In the final act, Mullen is confronted with an impossible choice: protect his daughter and the corrupt government figures involved, or uphold the truth. After initially agreeing to cover up the involvement of his daughter and other politicians, Mullen has a moment of clarity. 

In his climactic speech, he decides to expose the full truth, revealing the conspiracy to the world, including his daughter’s role in the attack. This decision not only undermines his family but also shakes the very foundation of the nation’s leadership.

The series ends with Mullen delivering an emotional, and morally charged, address to the Senate. Despite the political ramifications, Mullen’s actions affirm his commitment to honesty and integrity. The country may never fully recover from the revelations, but Mullen’s decision sets a powerful precedent for truth in the face of power.

Zero Day is now streaming on Netflix.