The trivia items below may give away important plot points.
This episodes contains several references to the 1988 graphic novel "The Killing Joke": -The quote "All it takes is one bad day to drive the sanest man to lunacy." -Jeremiah unexpectedly shows up at the Wayne Manor and shoots Selina. It's similar to how The Joker shot Barbara Gordon (Jim's daughter). -Bruce is forced to witness what looks to be Alfred's torture by Jeremiah's followers. It's similar to how Jim Gordon was forced to witness his daughter's torture and possible rape by the Joker. -Barbara Kean states that she liked the clock tower and calls its destruction a shame. After the events of the novel, Barbara Gordon took on the alias of Oracle and began using the clock tower as her headquarters.