Watch Dogs (video game)/Plot

In 2012, Chicago becomes the first city in the world to implement ctOS (central Operating System) – a computing network connecting every device together into a single system, developed by technology company Blume. In October, hacker Aiden Pearce and his mentor and partner, Damien Brenks, conduct an electronic bank heist at the high-end Merlaut Hotel in Chicago and trigger a silent alarm set by another hacker. Brenks tries to find the hacker, giving himself and Pearce away. Fearing for his family, Pearce drives them to safety in the guise of a surprise trip to the country. On the way, hitman Maurice Vega fires a gunshot which causes Pearce to crash the car; Pearce's niece Lena lapses into a coma and dies shortly after.

A year later, Pearce tracks down Vega at a baseball stadium in Chicago's Parker Square district. After a fruitless interrogation about Vega's contractor, he leaves Vega in the hands of his partner, fixer Jordi Chin. During his investigation, Pearce is approached by Brenks, who requests that he help him find the other hacker from the Merlaut job. After Pearce refuses, Brenks retaliates by kidnapping his younger sister Nicole, which forces Pearce to comply with Brenks' demands. With the help of Clara Lille, a member of the hacking syndicate DedSec that is fighting against Blume, Pearce tracks down the second hacker—gang leader and Army veteran Delford 'Iraq' Wade—and obtains a data sample from Wade's servers. He and Lille discover that Wade has information on almost every citizen of Chicago, protecting his gang from the authorities.

When they come across encrypted data beyond Lille's ability, she tells Pearce to find legendary hacker Raymond 'T-Bone' Kenney, who caused the Northeast blackout of 2003 while trying to expose the dangers of ctOS, which led to the system's implementation. After meeting Pearce and having him complete several tasks for him, Kenney agrees to help decrypt the data. Pearce assaults Wade's compound and downloads its server data, killing Wade when he confronts him. However, another hacker, JB "Defalt" Markowicz, infiltrates their system, steals the information and deletes it from their servers. Markowicz leaves a recording that discloses Lille's involvement in locating Pearce and Brenks during the Merlaut job, which resulted in Lena's death. Pearce angrily tells Lille to leave. When the authorities later confront Brenks about the loss of the server data, he tells them Pearce's identity. Meanwhile, Pearce and Kenney find and take down Markowicz, retrieving the data.

Pearce discovers where Nicole is being held, rescues her, and gets her and her son out of town for safety, while Kenney finds the contractor who ordered the hit on Pearce: Irish Mob boss and Merlaut owner Dermot "Lucky" Quinn. Pearce confronts Quinn, shutting off his pacemaker by hacking it. The dying Quinn reveals that he ordered the hit because he thought Pearce was searching for secret video footage of Mayor Donovan Rushmore, who accidentally murdered his secretary when she learned of his dealings with Quinn and threatend to expose them. After Quinn dies, Brenks calls Pearce to tell him that Lille offered to trade herself in for Nicole, and that Quinn sent hitmen to eliminate her for being a liability. Pearce rushes to save Lille, only to witness her being gunned down by the hitmen. After Pearce uploads the video of Mayor Rushmore, driving him to commit suicide, Brenks, who has also hacked ctOS, uses the system to wreak havoc in the city. With Kenney's help, Pearce infects ctOS with a virus that shuts down the system, causing a citywide blackout, and finds Brenks, who is hiding in a lighthouse. Chin arrives, claiming to have received a contract to kill both men, but Pearce injures him and kills Brenks. Chin later calls Pearce one last time to tell him where Vega is kept; Pearce heads there, and decides his fate.