- "All it takes is one bad day to reduce the sanest man alive to lunacy. Jerome gave me what I thought was the worst day of my life. But only by losing everything was I able to face what was inside me. And I believe I've seen something very special - inside of you as well. But, to free it, you'll have to lose everything and everyone you hold dear."
- —Jeremiah Valeska to Bruce Wayne
As Gotham falls into complete anarchy, a team of unlikely heroes step up to save it. Bullock takes the lead at the GCPD and Bruce's psychological limits are tested as those close to him are put in danger.
Jeremiah Valeska positions the energy generator bombs around Gotham City and gives the citizens six hours to evacuate the city. Before escaping the bunker, Jim Gordon managed to take the blueprints for Jeremiah's plans. Knocked out during the explosion, Gordon is rescued by Lee Thompkins and Edward Nygma.
Alfred Pennyworth is captured by Jeremiah, and used as bait to lure Bruce Wayne into a trap. Jeremiah uses Scarecrow's fear toxin to make Bruce believe Alfred has been driven insane. Alfred attacks Bruce, and Bruce is forced to kill him. However, Selina Kyle frees the real Alfred, and show Bruce that he has been tricked.
Oswald Cobblepot and Solomon Grundy join forces with Barbara Kean and Tabitha Galavan to take on Jeremiah. Cobblepot's torture of one of Jeremiah's followers led him to discover that the bombs were connected by a core relay. The group of villains demand a ransom from Jeremiah or threaten to destroy the relay. Jeremiah destroys the relay instead and rewires the bomb to detonate in sequence.
Gordon and Nygma study the blueprints and soon realize that the bombs are placed to destroy certain parts of the city and create a maze. Gordon knocks out Nygma and gets the plans to the Gotham City Police Department. Working with Lucius Fox, Harvey Bullock gets to the first bomb and manages to disarm it in time.
Jeremiah's plans are foiled, but he is approached by Ra's al Ghul. Ra's proposes an alliance, which Jeremiah accepts. At Wayne Manor, Bruce, Selina, and Alfred are recovering when Jeremiah breaks in and shoots Selina in the abdomen.
- This episode takes place on the same day as "A Dark Knight: That Old Corpse", since Jeremiah's bunker was just blown up a few hours ago.
- The title of the episode references the Joker’s infamous line in The Killing Joke comic: ”All it takes is one bad day to drive the sanest man to lunacy.” As such, the episode takes inspiration from the story in several ways:
- Bruce being forced to witness what looks to be Alfred's torture by Jeremiah Valeska's followers is similar to how Jim Gordon was forced to witness his daughter Barbara Gordon's torture and possible rape by the Joker in the original story.
- Jeremiah wears a hat that resembles what the Joker wore in the comic during his pre-Joker flashbacks as well as the present day segments.
- The characters in the episode discuss the infamous line a few times, paraphrasing it in various ways, with Bruce and Jeremiah even crafting their own respective interpretations of its meaning.
- Jeremiah Valeska unexpectedly showing up at the Wayne Manor, pressing his gun at Selina Kyle's waist and shooting her, leading to her falling on the table is a refernce to how Barbara Gordon was shot by the Joker in the comic.
- The hallucination that Bruce sees where Alfred is dosed with Laughing Gas is a possible nod to his Earth-3 counterpart, Outsider, who was also dosed by Joker with the Joker toxin.
- Barbara Kean states that she liked the Gotham Clock Tower and calls its destruction a shame. This is an allusion to the DC Comics, in which her and Jim Gordon's daughter Barbara Gordon used the Gotham Clock Tower as her headquarters when she took on the alias of Oracle following the events of Batman: The Killing Joke (May 1988), where the Joker paralyzed her from the waist down with a gunshot.
- Jeremiah Valeska meets Oswald Cobblepot, Butch Gilzean, Barbara Kean, Tabitha Galavan and Ra's al Ghul.