When they are given the Social Security number of a teenager who was killed two years ago, Reese and Finch begin to question the infallibility of The Machine. Meanwhile, Finch flashes back to The Machine's origin and how it was developed.
Ghosts, in famous folklore, are defined as dead spirit that reappear in front of a living person either with malevolent or benevolent intention. The most obvious meaning would be Theresa Whittaker's false deceased status and how it continues to destroy her life, but the title can also refers to Finch's best friend Nathan Ingram, whose death continues to haunt him to this day as well as Finch's decision to intentionally ignored the irrelevant list caused the death of many people and haunt the live of their love one, most notably Jessica Arndt.
Beginning with this episode, a "saga sell" title sequence is used. The opening features previously seen moments from "Pilot", this episode, and "Mission Creep", with Michael Emerson's voice over, and is designed to introduce the premise of the show to viewers. It is not unusual for such elements to be introduced in the second episode, which is the first to reflect changes made in response to the pilot.
Reese's now iconic black suit with a white shirt first appears in this episode. Early in the episode, he wears a dark grey shirt, which changes to a lighter grey one later in the episode. At the end of the episode, he is first seen wearing a white shirt with his black suit. Although the black suit and white shirt did not become a constant until "Judgment", this episode features the early evolution of his trademark attire.
In the tracking shot at the beginning of the second flashback, the servers are computer generated.
Interview notes collected by Maxine Angelis in her search for the man in a suit ("Bury the Lede") confirm that Reese did not kill the assassins in the elevator but only knee-capped them, as implied by Detective Terney.
Reese shoots three people, one of them, the hit man, twice.