While officially the 17th episode of Season 4, "Requiem" is a pivotal origin story often grouped with mid-season highlights. It focuses on the backstory of (Kathryn Nemec) and her history with Katarina Rostova and Masha (Liz).
(Season 4, Episode 17 / Often cited as S4E8 in specific contexts) [S4E8] Requiem
: Titled "Gold, Glory & Custer: Requiem Part II," this episode is praised by history buffs for its authentic use of Lakota dialogue and historical figures like Chief Touch the Clouds. While officially the 17th episode of Season 4,
: This detailed article from Pop Culture References explores how the episode serves as a major clue to Reddington's true identity, showing Kathryn's life as Liz's nanny and her initial bond with Katarina. : This detailed article from Pop Culture References
(Video Game): While not a TV episode, this recent release has generated significant discussion regarding its ending and the character Grace.