Comissioner Gordon goes to the dentist as part of a required health checkup, voicing his displeasure all the while, when it's revealed that SelfDemonstrating/TheJoker has taken the place of his dentist in order to kill him. Fortunately for Gordon, Franchise/{{Batman}} busts in, revealing that he got a clue with this latest plan with a chattering teeth toy, and Batman saves him. Seemingly just to rub it in, Batman takes the time to tell the Joker he finds the chattering teeth gag uncreative.

The Joker is later seen at his lair in an abandoned toy factory trying to come up with a new plan. Harley tries to seduce him and give her own ideas, but The Joker angrily blows them off. The Joker then finds one of his scrapped plans to kill Batman in a tank of piranhas, but he then remembers that he couldn't get the piranhas to smile, ruining the joke potential. Harley tries one last attempt at seducing The Joker, but gets kicked out. Harley laments her plight at not being able to have a relationship with her puddin', and concludes that Batman is responsible for this.

Harley then flashes back to the time when she was just Dr. Harleen Quinzel, an intern at Arkham Asylum. The Joker left a card and rose in her office, so Harleen goes to see him. The Joker's initial attempts at courting Harley are unsuccessful, until he offered to tell Harley his biggest secrets. Harley then set up an appointment with The Joker, confident that his tricks wouldn't work on her. Unfortunately, The Joker's fabricated sob story was able to win her sympathy.

One day, when Batman captured The Joker after one of his capers, Harley decided to steal several pieces of merchandise from a novelty store. She adopted these paraphernalia as part of a new supervillainess identity. She broke The Joker out of his cell, adopting the name Harley Quinn as suggested to her earlier.

Back to the present, Harley plots to get rid of Batman so she can finally be with her puddin'. She sends a tape in order to lure Batman so he can be captured, and she succeeds.

Batman, captured by Harley, wakes up above a tank of piranhas, just like The Joker plotted. Harley had the idea of hanging the victim upside down so that the fish look like they're smiling. Harley tells Batman that successfully killing him will be a testament of her love to the Joker, meaning the two can finally settle down. Upon hearing this, Batman first reacts with disbelief and then, surprisingly, laughs at the idea and tries to convince Harley that The Joker lied to her and used her. Harley, angered by Batman's arguments, tries to drop him into the tank, but Batman convinces Harley to call The Joker, saying that he won't believe Batman's dead unless he sees it.

When The Joker arrives on the scene, Harley happily points out how she modified his plan to make the fish smile. The Joker reacts by angrily beating and berating her, reminding her that he wants to be the one to kill Batman and that she shouldn't explain the joke or else there is no joke. Harley is then thrown out a window, and she lands in a container. Injured and barely conscious, she feebly cries that it is all her fault for not getting the joke. The Joker then unhangs Batman from above the tank, just before he realizes that he has the opportunity to kill Batman. Batman then escapes by breaking the tank open and quickly grabbing his belt, picking the lock and escaping. The Joker makes a run for it, and Batman then chases him to the top of a train, explaining that his BatmanGambit was the only way to get out, and that Harley came closer to killing him than The Joker ever did. The two then fight on top of the train, ending with Batman hitting the Joker off the train and into a smokestack, causing him to take a seemingly lethal fall.

Back to Harley, she is injured and incarcerated in Arkham, the very place she interned at. She thinks to herself, in her old voice, that she sees The Joker for what he really is, and wants nothing more to do with him. But in her cell she sees a rose with a "Feel Better Soon" card from him, revealing that he survived the fall, and she falls in love with him again.

This episode was adapted from an Eisner Award-winning issue of ''ComicBook/TheBatmanAdventures'', the tie-in comic of ''WesternAnimation/BatmanTheAnimatedSeries''.
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!!Tropes
* ActorAllusion: SelfDemonstrating/TheJoker says to Franchise/{{Batman}}, "[[Creator/MarkHamill May the]] [[Franchise/StarWars floss be with you.]]"
** A double allusion, as Hamill's wife is a dental hygienist.
* AdaptationExplanationExtrication: While she doesn't deserve how she ends up in either version, the comic starts off by showing character flaws of Harley's that aren't shown in the cartoon, which make it seem like her fall was in part due to her own weak will and character and not just the Joker's manipulation. In college she would "improve" her grades by bedding her professors and was only trying to get into the psychology field to make money as a quack pop psychologist.
* {{Backstory}}: For Harley Quinn.
* BatmanGambit: Batman escapes by getting Harley to call The Joker, as Batman knows only The Joker would want to kill him.
* BigDamnHeroes: Just another night of work for Franchise/{{Batman}}.
* BillBillJunkBill: The Joker rejects possible capers as being "Boring. Lame. Not funny. Been done. Too Riddler!"
* {{Bowdlerization}}: Harley's questionable academics in her college days aren't mentioned in the cartoon. There's also a pool of blood forming around Harley after the Joker throws her out the window in the comic; her injuries in the cartoon are all internal.
* ChronicVillainy: All it takes is a single rose and a note from Mr. J for Harley's brief attempt at redemption to fall apart.
* ContinuityNod: The Joker remembers his plan to feed Batman to smiling piranhas, which he had to scrap as he couldn't get them to smile, noting that they were even immune to his scheme from "The Laughing Fish."
* DontExplainTheJoke: Discussed by The Joker, "If you have to explain the joke, there is no joke!"
* EvilLaugh: Surprisingly, Batman gives one out, since the idea of Harley being with The Joker is just that ridiculous to him.
* FirstNameUltimatum: Joker shouting: "HAAAAARRRR-LEEEEY!"
* {{Flashback}}: How Harley's backstory is revealed.
* FoeYay: InUniverse, Harley recognizes this as the reason why she must MurderTheHypotenuse Batman.
* FreudianCouch: We see a montage of how Harley Quinn met The Joker while she gave him psychoanalysis. It starts with him on the couch, but as he twists her mind, later scenes have the Joker as the psychiatrist, with Harley on the couch.
* IgnoreTheFanservice: The Joker to Harley.
* KirkSummation: Batman gives one to The Joker on top of the train, explaining that his BatmanGambit was the only way he could have escaped.
* MadLove: Adapted from the TropeNamer.
* MultipleChoicePast: The Joker has millions of stories to tell to anyone willing to listen.
* MurderTheHypotenuse: This is Harley's truly deranged goal: Without [[FoeYay the Batman, the Joker]] could be hers at last!
* NeverBringAKnifeToAFistFight: A very enraged Joker attacks Batman, and seems to be giving him more trouble in a fistfight than he usually does... until he pulls out a knife, and Batman instantly knocks him off the train.
* NoOneCouldSurviveThat: The Gotham news believes The Joker couldn't have survived falling into that smokestack. [[JokerImmunity They're wrong]], since The Joker survived to give Harley another rose with a card.
* TheOnlyOneAllowedToDefeatYou: Why The Joker is so angry at Harley for pulling off one of his plans.
* OriginsEpisode: For Harley Quinn.
* OutGambitted: Harley Quinn actually gets Batman to fall for one of her traps, but then he uses a [[BatmanGambit him gambit]] to exploit both her feelings for the Joker and how the Joker would react.
-->'''Batman''': She almost had me, you know. Arms and legs shackled, dizzy from the blood rushing to my brain... I had no way out other than convincing her to call you. I knew [[TheOnlyOneAllowedToDefeatYou your massive ego would never allow anyone else the honor of killing me]], though I have to admit she came a lot closer than you ever did, ''puddin'.''
* TriangRelations: Type 5: Harley {{MadLove}}s SelfDemonstrating/TheJoker, but the Joker {{FoeYay}}s Franchise/{{Batman}}. Batman doesn't have feelings for either. Harley tried persuading the Joker to WhyDontYouJustShootHim Batman. It didn't work, so Harley being an AxeCrazy ClingyJealousGirl attempts to MurderTheHypotenuse.
* SeriesFinale: For the whole ''BTAS'' collection. (In airing order, in production order Judgment Day was the last to be produced.)
* SexualExtortion: In the comic, Harley would have sex with her professors to raise her abysmal grades.
* SharkPool: Done with piranhas. The Joker had concocted it as one of his many potential ways of eliminating Batman, but gave up on it because there was no way to make it funny. He had wanted to call it the "Death of a Thousand Smiles", but piranhas are incapable of smiling, even when given Joker-Venom. Harley Quinn tried to implement the plan herself to impress him, reasoning that the frowns would ''look like'' smiles if you lowered Batman into the tank upside-down. Joker was furious, however, because [[DontExplainTheJoke she had to explain the joke]].
* ShoutOut: The frame of Harley's backstory is almost identical to Clarice Starling's in ''SilenceOfTheLambs''. Young impressionable Psychiatrist/FBI agent in training is sent to psychoanalyse a psychotic killer and instead is disarmed and [[HannibalLecture psychoanalysed by the killer himself]]. Much like Starling, Harley is implied to be hiding her much lower class accent.
* SnapBack: Harley gives up on the Joker at the end, and then falls back in love with him just as the episode concludes. Entirely in character - see ChronicVillainy above.
* StatingTheSimpleSolution: Harley asks the SelfDemonstrating/TheJoker "WhyDontYouJustShootHim" in regards to dealing with Batman.
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