It's Chicago, 2035, and homicide detective Del Spooner (WILL SMITH) is one of the few people alive who don't like the preponderance of robots that have infiltrated everyday life from being personal assistants to garbage collectors. It's only going to get worse as U.S. Robotics CEO Lawrence Robertson (BRUCE GREENWOOD) is about to deliver the newest and most advanced generation of such machines the world has ever seen.
Yet, when top U.S. Robotics executive Dr. Alfred Lanning (JAMES CROMWELL) ends up dead following a long fall from his office window, Del is called to the case by a preprogrammed hologram of Lanning. While it can only answer specific questions, Del soon believes that his former acquaintance not only was trying to get some information to him, but also that he didn't commit suicide like everyone else thinks, but was murdered.
Robertson and Del's boss, Lt. John Bergin (CHI McBRIDE), think that's nonsense, particularly since Lanning's room was locked from the inside. Nevertheless, and when accompanied by the company's programmer, Susan Calvin (BRIDGET MOYNAHAN), Del suddenly finds his chief suspect hiding in Lanning's office.
And it's none other than one of the new USR robots that calls itself Sonny (ALAN TUDYK). The robot flees the scene and is captured, but no one except for Del thinks it committed the crime. That's because Lanning imbued every robot with three basic laws and guiding principles that prohibit and prevent them from harming humans.
Even so, Del sees something quite different in Sonny and has a bad feeling about what's about to occur. As he continues his investigation, the detective soon realizes even he underestimated the problem that's about to unfold for all of humanity.