: For a broader look at the secrets revealed during this era of the show, the Raymond Reddington Wikipedia page summarizes the "imposter" theory and the role Kathryn played in hiding the truth.
: The X-Files Wikipedia overview notes how this episode transformed Special Agent Dana Scully from a skeptic into a "reluctant believer" after Mulder's disappearance. Other Shows with an Episode 8 Titled "Requiem" [S4E8] Requiem
(Season 7, Episode 22 / Sometimes confused with S4) : For a broader look at the secrets
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). [S4E8] Requiem