While season 5, episode 7 is actually titled "O Come, All Ye Faithful," the episode titled " What's Past is Prologue " is the landmark 100th episode of the series and is officially Season 5, Episode 8 . Directed by Tom Cavanagh (who also plays multiple versions of Harrison Wells), the episode is widely praised for its nostalgic trip through the show's history. Key Review Highlights
The Flash Season 5 Episode 8 Review: What's Past is Prologue [S5E7] What's Past is Prologue