TNG Season 2 Episode 9: The Measure Of A Man

From one episode that is crucial to others but considered purely on its own merits is a debatable entry on this list, to an episode that absolutely belongs in the top 2 stories – and one that rivals even Best Of Both Worlds (yes, I said it!)
Data is ordered to undergo dismantling so that Commander Maddox of the Daystrom Institute can study him. Data is not comfortable with that and refuses, only to find his final recourse to resign isn’t an option to him as he is seen by Starfleet as property. Cue the best courtroom drama episode of Star Trek ever produced including an astonishing performance from Patrick Stewart backed up by an understated but incredibly potent interaction with Whoopi Goldberg, and superb work from Jonathan Frakes, especially in the Blu-ray exclusive extended versions of the story.

Plot

While the Enterprise is visiting Starbase 173 for routine maintenance, cyberneticist Commander Bruce Maddox (Brian Brophy) comes aboard to pay a visit to Lt. Commander Data (Brent Spiner), wishing to better understand Data's positronic brain. It quickly becomes clear that Maddox has an ulterior motive of transferring the contents of Data's memory to the starbase mainframe computer and shutting down and disassembling him to learn how to recreate the technology. Though Maddox promises to restore Data following his analysis and assures him his memories will be intact, Data is concerned that the procedure is riskier than Maddox is letting on, and argues that while the factual details of his memories will be preserved, the nuances of his experiences may not be. Data refuses, causing Maddox to turn to Starfleet to order him to comply. Captain Jean-Luc Picard (Patrick Stewart) supports Data's position, and is advised that the only way for Data to evade the order is to resign from Starfleet, which Data does. Maddox, however, argues that Data is Starfleet property, not a sentient being, and as such does not have the right to choose to resign.
Meanwhile, Picard has to deal with the presiding Judge Advocate General for the sector, Captain Philippa Louvois (Amanda McBroom), who was a former love interest until she aggressively prosecuted Picard in a court-martial involving his actions on the USS Stargazer. When Louvois rules for Maddox, Picard requests a formal hearing to challenge the ruling. Louvois agrees, and allows Picard to represent Data during the proceedings. Due to a shortage of qualified legal staff, Louvois compels Commander William Riker (Jonathan Frakes) to represent Maddox. Riker's arguments portray Data as merely a machine constructed by man, and no more than the sum of his parts. In a striking final demonstration, Riker activates Data's "off switch", causing the android to shut down. Picard calls for a recess, during which he meets in Ten Forward with Guinan (Whoopi Goldberg), who suggests that regardless of whether Data is a machine or not, Maddox's plans for reproducing him would lead to a situation tantamount to slavery. Picard uses this to defuse Riker's arguments, and turns the discussion to metaphysical matters of Data's sentience, using Data and Maddox as witnesses. Picard points out that Data meets two of the three criteria that Maddox uses to define sentient life. Data is intelligent and self-aware, and Picard asks anyone in the court to show a means of measuring consciousness.
With no one able to answer this, Louvois acknowledges that neither she nor anyone else can measure this in Data and rules that he has the right to choose. Upon the court's ruling, Data formally refuses to undergo the procedure. After the hearing, Data clearly holds no ill will against Maddox; Data reminds the scientist that his work remains intriguing, and offers to assist in further research after Maddox has had more time to study and perfect his techniques. Maddox, for his part, refers to Data for the first time as "he" rather than "it". Later during a party celebrating Data's victory, Data finds Riker alone in a conference room, ashamed of having had to argue against his friend in the hearing. Data cheers him up by telling him that his action was an act of self-sacrifice that gave Data the chance to win his freedom, as had Riker refused to participate, Louvois' original judgement in favor of Maddox would have been final. The two then happily return to the celebration together.