Charles Nichols is a Dutch-American doctor who worked at a pharmaceutical company, Devlin MacGregor and was a trusted friend and former colleague of Dr. Richard Kimble (the protagonist of the film).
Upon finding out that Richard had discovered that Devlin MacGregor's new drug Provasic was causing liver damage, which would've prevented it from being approved by the FDA and not wanting to let Richard to the truth that would end the project, Nichols sends one of his security guards Fredrick Sykes, who has a prosthetic right arm, to Richard's home to kill him after he borrowed his car and called Sykes with the phone in his car. However, only Richard's wife Helen was there, so Sykes ends up brutally beating and murdering Helen and disappears, leaving Richard to take the fall for the murder and receive the death sentence for it. Nichols also frames his deceased colleague, Dr. Alec Lentz as the one who set up the murder. During the film, Nichols supports Richard in the time that he is on the run and refuses to give Deputy Marshal Samuel Gerard any information that would lead to Richard's capture, hiding the fact that he's directly responsible for Helen's death and Richard's framing to begin with.
A few days later, Nichols receives a phone call from Richard, who claims he found the ones responsible for Helen's murder: Devlin MacGregor and Lentz. Nichols tells Richard that Lentz died in a car crash around the time of Helen's murder. Later, Richard does some research on the liver tissue sample with Dr. Kathy Wahlund, who tells Richard that they've been tampered with, and they all came from the same healthy liver. Richard asserts his theory that it was Lentz, but Dr. Wahlund notes that half of the samples that he approved of were done so on the day that he died. Thinking someone with access to Lentz may have been behind this, Richard immediately realizes that this whole time it was Nichols himself, and goes to confront him.
After Richard escapes a transit train after handcuffing Sykes to a pole there, he goes to the hotel where Nichols is giving his speech in regards to the approval and release of Provasic. Nichols attempts to usher Richard quietly into a small suite off to the side of the conference room, but Richard vocally accuses Nichols regarding his motive: Dr. Nichols falsified his research, orchestrated Helen's murder, and most likely killed Lentz before framing him.
Once in the suite, Nichols attacks Richard, and the two scuffle in the room, before it eventually spills out onto the hotel's rooftop. Gerard arrives but is told to stay out of the situation by the CPD. Gerard storms past the CPD and he eventually finds where Richard went. Gerard then makes his way to the rooftop and watches as Richard and Nichols fight, before plummeting through a skylight, and falling atop an elevator that then descends.
The chase eventually leads them to the hotel's laundry room on the fifth floor. Nichols, who landed in front of the doors, recovers from the fall first, but Richard is soon behind him as are Gerard and Renfo who make it to the fifth floor and clear out the staff. Gerard yells out to Richard and tells him that he's not only trapped, but the CPD thinks that he killed an officer on the train and if he doesn't give himself up, he'll be shot on site. Gerard also says that he knows of Richard's innocence, as well as what really happened on the night of his wife's murder: Nichols had borrowed Richard's car and he had the keys to his house, which was how Sykes got in without forced entry and he also telephoned Sykes from Richard's car. Nichols manages to knock out Renfro with a hanging gurney and then takes his gun to shoot Gerard, but Richard takes a steel pipe and knocks him out.In the aftermath, Sykes and Nichols are taken into custody, and Gerard escorts Richard out of the hotel in handcuffs. In the back of their car, Gerard removes the handcuffs, and gives Richard a small bag of ice for his bruised hands. The car then pulls away as Richard is being driven off to be exonerated while Nichols and Sykes are taken to face charges for their crimes and presumably receive the death sentence that was originally for Richard.