At around the 08:45 mark, when Frank is ascending the stairs at the FBI, you can see what looks to be Fox Mulder and Dana Scully descending the stairs next to him. It is unclear if they are the actual actors who play the roles. Mulder and Scully are the main characters of the X-Files, another series created by Chris Carter.
First appearance in the series of the show's main villain, Lucy Butler, played by Sarah-Jane Redmond.
The last episode in the series that Chris Carter wrote solo. From here on in, he would work in tandem with Frank Spotnitz.