Set in present-day London, Zero Days uses cybersecurity concerns to create the novel’s central mystery: who killed Gabe Medway and why. Gabe and the protagonist, Jack Cross, are computer experts who assess the security of companies that hire them, with a focus on how well protected clients’ data is. Gabe is a coder who looks for security vulnerabilities (zero-days) in apps. The discovery of one such flaw (which was in fact a deliberate security hole to facilitate cybercrime) leads to his murder. None of these occupations existed until recently, as the first mobile app was created in 1993. Concerns about the privacy of mobile phone users have only increased since then.

In her quest to find her husband’s killer, Jack relies on social media to investigate the security practices of Sunsmile Insurance and publicize Gabe’s findings. She uses multiple “burner” phones that cannot be traced by police and creates Wi-Fi hotspots so that she can access the internet. She employs Signal, an encryption app, to contact her sister. Finally, she livestreams her confrontation with Cole, leading to her exoneration. Even the novel’s title refers, at least in part, to the security flaw that Gabe is murdered to conceal.