Mumbai is in a state of chaos. All traffic signals across the entire city have stopped working.
Shahwaz Ali Mirza head of the Maharashtra Anti-Terrorism Squad receives an anonymous email claiming it to be a Distributed Denial of Service (DDoS) attack. He quickly puts together a crack team that includes his protege IG Cybercrime Vikrant Singh and gets to work trawling the dark web for more information on this mystery attack. However a move to bring forward the hacker backfires leading to a second deadlier attack on Mumbai's lifeline the railway system.
It is their first brush with cyberterrorism: a zero-day vulnerability in the Indian government's system that could bring the country to its knees. Racing against time and investigating a case unlike any other in Zero Day Mirza and Vikrant face the most dangerous Paper Backsion of their lives.