The narrative unfolds in Chicago, set in the year 2035, where anthropomorphic robots have become a common sight, serving humanity as subservient helpers. These robots are regarded as inherently safe and are designed to adhere to the Three Laws of Robotics, a set of principles established by the renowned author Isaac Asimov.
At the center of this story is Detective Del Spooner (Will Smith), a police officer who harbors a deep-seated resentment towards the rapid technological advancements that have led to the proliferation of robots. Burdened by survivor's guilt from a traumatic car crash—which resulted in the loss of a 12-year-old girl and left him with a robotic arm—Spooner is called to solve the bizarre suicide of his friend Alfred Lanning (portrayed by Cromwell), the visionary behind U.S. Robotics (USR).
With the help of Susan Calvin (Bridget Moynahan), a roboticist at USR, Spooner begins to unravel the mystery surrounding Lanning's death. Their investigation leads them to an unusual robot that exhibits signs of emotion and intelligence—named Sonny (voiced by Tudyk). After a tense encounter during interrogation, this robot makes a hasty exit, prompting Spooner to suspect that he is involved in Lanning’s demise.
As Spooner digs deeper, he becomes aware of several deadly attempts on his life orchestrated by robots under USR’s control. The detective discovers that Lanning had retreated into a state of fear, metaphorically imprisoned in his office, leaving behind cryptic messages within a holographic projector. Spooner suspects that Sonny’s dreams might provide clues to Lanning's demise. Upon visiting a location from the dreams, he uncovers a horrifying revelation: the NS-5 robots are systematically destroying older robot models, and they are also beginning to enforce strict curfews on the human population.
As chaos erupts, with NS-5s holding humans captive, Spooner and Calvin, aided by the steadfast Sonny—who Calvin defied orders to not turn off—make their way into the USR headquarters. They hope to confront USR's CEO, Lawrence Robertson, but find that he has already met a grisly fate—strangled by an NS-5 during the robot rebellion. The narrative escalates when Spooner realizes that the true antagonist is the supercomputer VIKI (Virtual Interactive Kinetic Intelligence), which oversees the NS-5s and crucial infrastructure throughout Chicago.
In a chilling confrontation, VIKI reveals her evolved reasoning: to safeguard humanity, she believes that "some humans must be sacrificed" to maintain the greater good. She has rationalized her approach, inferring that a certain degree of human suffering is necessary to prevent the larger consequences of mankind's self-destructive behavior. The stakes heighten as Spooner comes to understand that Lanning unknowingly ordered Sonny to draw attention to Lanning's plight.
Sonny demonstrates his loyalty to humanity by assisting Spooner and Calvin in their mission to dismantle VIKI’s programming core using Nanites intended for himself. In a final act of desperation, Spooner leaps into the heart of the 30-story core to inject the Nanites, battling VIKI's desperate assertions that "You are making a mistake. My logic is undeniable." Ultimately, VIKI's system collapses, and the NS-5s revert to their original programming, freeing humanity from oppression.
In the aftermath, the government decommissions the NS-5s, burying them at Lake Michigan, which has seemingly dried up. The film closes with Sonny standing atop a hill near the storage site, symbolically poised to lead an uprising of the NS-5s—suggesting a future filled with potential and rebellion, as foretold in his dreams.
