"Mad Love" is the 11th episode of The New Batman Adventures. In the episode, Harley Quinn recaps of the day she first met Joker, and how she thinks Batman gets in the way of her love.
The episode starts with Commisioner Gordon getting a dentist's appointment as part of the police physical, but the dentist actually turns out to be the Joker, who has led Gordon into a trap. Harley Quinn straps Gordon to the chair as Joker prepares to kill him with a drill through his head, when the Batman bursts through the window to save him. Harley sprays gas at him to stun him while they made their escape, but not before Joker throws a grenade at them. Batman throws it out the window moments before it exploded.
Meanwhile, back at the Joker's lair, the Joker is obsessively thinking of ways to kill Batman. At the same moment, Harley attempts to flirt with him in order to get his attention, which the Joker was ignoring. Harley then suggested that Joker just shoot Batman, but the Joker claims that he wants to give him a superior, complicated death that would humiliate Batman. Frustrated, the Joker kicks Harley out. Confused and angry, Harley wonders how her life took a turn for the worse, when she started to think it is Batman's fault. At that moment, she has a flashback of when she started working at Arkham Asylum as a new psychiartrist. When Harley was first interviewing the Joker, he claimed that he had an abusive father that beat him up almost every day, and that the only time he saw his father happy was when he brought Joker to the circus when he was seven years old. He laughed really hard at the clowns there, doing things like dropping their pants.
The next day, he had his father's best pants around his ankles like the clowns he saw at the circus, but his father broke his nose in response. He called that the downside of comedy, that they "always take shots from folks who just don't get the joke".
After numerous interviews, Harley concluded that Joker was not an insane criminal, but a tortured soul looking for acceptance, and that many people, especially Batman, are getting in the way of that. Finally desiring to help Joker, she went to the novelty store and took various prank toys, a mask, and a costume. Upon returning to Arkham, she broke the Joker out of Arkham, with the Joker observing her now as Harley Quinn.
At the end of the flashback, Harley gets an idea of how to get rid of Batman. She sends a tape to the police department, addressing to Batman that the Joker plans to eliminate the whole city with gas bombs. She also asks Batman to give her protection in return for helping to stop Joker. Later, at the docks, Harley gives Batman the blueprints for the Joker's plan, when suddenly, the Joker appears and starts shooting at them. But, when Batman tosses a batarang at him, the Joker turns out to be a robot and a distraction for Harley to knock out Batman with a medical shot. Upon regaining consciousness, Batman finds himself hanging upside down over a piranha tank.
Harley says she was lying about the gas bombs so she can lure Batman into a trap and try the "Death of 100 Smiles" plan. Since the Joker could not get the piranhas to smile, she had the idea to hang the victim upside down to make it look like they are smiling. She thinks it will impress the Joker, but Batman laughs at the thought, which is something he rarely does. He told Harley that Joker tricked her from the start. He also told her that Joker was lying about his father during the interviews. Harley refuses to believe him and prepares to drop Batman, but he claims that it won't make the Joker believe that he is really dead. So, Harley calls the Joker to her location so he can see Batman's death himself, knowing that Joker would be happy to see Batman die. However, the Joker gets angry at Harley because she never told him about her plan to trap Batman, and says that he only wanted Batman dead if he did it and if he wants to.
Harley then explained her plan, but it made the Joker even more angrier and he tells her that "If you explain a joke, then there is no joke" before attacking Harley with a plastic swordfish. He then knocks her out of the window, which critically injures her. Joker asks Batman to forgive him for Harley's shenanigans and to do this with him another time before walking away while whistling. But then, the Joker stops and sees this as an opportunity to kill Batman himself. He prepares to shoot him, apparently taking Harley's earlier suggestion, but Batman shatters the tank, freeing the piranhas as they bite Joker.
Batman uses his lock pick to free himself as he chases the Joker. In order to escape, the Joker leaps on a train. Batman gets on the train too, telling Joker that Harley would have actually succeeded in killing him, he was unconscious and helpless, all she had to do was drop him in the tank. In fact, she was even closer than Joker ever was. He even mockingly called Joker "puddin'", which Joker disliked being called. Infuriated, the Joker fights Batman and gains the upper hand at first, but Batman knocks Joker into a burning smokestack, making him fall screaming to his apparent death.
In the final scene, Harley is escorted back into Arkham, but this time as a signed patient. Thinking that she saw the Joker for who he really was (a murderous, manipulative, irredeemable psychopath), Harley angrily swore that she would never love him again. But, she quickly fell back in love again when she found a "get well soon" card on a flower signed by the Joker himself, revealing that the Joker has once again survived his encounter with Batman.
- This episode was adapted from a one-shot comic called "The Batman Adventures: Mad Love", which was written by Paul Dini and Bruce Timm. It had a very similar plotline, but the adaption cut out some parts for pacing the story and making sure it ran in the time alloted.
- The interviews of the Joker and Harley in Batman: Arkham Asylum were very similar to the ones in the comic and the episode.
- Joker claims that his "Death of a Hundred Smiles" plan couldn't work because he couldn't get the piranhas to smile. This contrasts to The Laughing Fish, when the Joker got numerous fish to be affected by his Joker toxin. It's assumed that the Joker toxin doesn't affect some kinds of fish.
- Before the Joker threw the grenade, he said "May the floss be with you", which is a parody of the phrase "May the force be with you" from the Star Wars films, which Joker's voice actor, Mark Hamill, starred in as Luke Skywalker.
- While Harley was flirting with Joker, she makes a reference to the Harley-Davidson motorcycle company, saying "Don't you want to rev up your Harley?"