In the Castle episode " Deep Cover ," Richard Castle's mysterious CIA operative father, Jackson Hunt, returns when a murder investigation reveals a plot involving stolen agent identities. Castle helps his father recover a "burn list" from a ruthless assassin, deepening his understanding of his father's dangerous, secretive life before Hunt vanishes once again.
You can watch Castle Season 6, Episode 12 on Apple TV or read about it on the Castle Wiki . Deep Cover | Castle Wiki | Fandom [S6E12] Deep Cover