Stephanie Goldmark (Laurie Fortier) is the main villainess from "The Greater Good," episode 6.19 of Castle (airdate March 24, 2014). She is an AUSA attorney who was introduced as being part of the investigation of stock trader Peter Cordero's murder.
Stephanie appeared with fellow AUSA attorney Elizabeth Weston (the sister of NYPD captain Victoria Gates) and they revealed that Cordero was part of their investigation into his boss, Jamie Burman. Burman was suspected of insider trading and securities, and regarding Cordero, Stephanie revealed that his arrest for cocaine possession forced him to cooperate and act as an informant in Elizabeth's investigation.
Because of this, as well as a revelation that Burman paid Cordero $25 million to throw the case, Burman was suspected in the murder. During his interrogation, Burman revealed that he knew about Cordero wearing a wire and that he left it at a dead drop before he was killed. Burman's statement contradicted a claim that Cordero had his wire with him while he was murdered, and it led to the truth at the episode's climax: Stephanie killed Cordero to cover up a previous villainous act she committed.
After Elizabeth stated that she needed someone on the inside to catch Burman, Stephanie turned heel by enlisting a cop to plant the aforementioned cocaine on Cordero. After his arrest, the villainess used it as a bargaining chip to force Cordero to act as an informant for the prosecution, but later on, Stephanie heard his recording before it was to be sent to analysis, which had Cordero venting over being set up to be arrested for drug possession despite following the rules and declaring that he was done. Afterwards, Stephanie engaged in an argument with Cordero at his home, which ended with the evil Stephanie shooting and killing Cordero, using his gun in the murder and making it appear that the wire was the motive in the killing.
In response to Elizabeth asking for the reason for her actions, Stephanie mentioned Elizabeth's need for an inside man, adding that her actions were for the greater good, a sentiment that Elizabeth disagreed with. Regarding the murder, Stephanie stated that she tried to reason with Cordero, but he wouldn't listen, and she was later arrested for her crimes.