In a prologue set in The Middle Ages, knight Jason Blood betrays his lord King Arthur due to his love for the villainous Morgaine Le Fay, who instantly betrays him with a poisonous bite as soon as he lets her and her son Mordred into the castle. Merlin decides that dying quickly is too good for Jason, however, and curses him to an immortal bond with the demon Etrigan until his crime is atoned.
In the present day, Jason has learned that Morgaine is searching for the powerful Philosopher's Stone, and asks his friend Batman for help. The search for the stone leads Jason/Etrigan and the Justice League to the house of archaeologist-turned-playboy Harvey Hickman, who's been using the stone's power to fulfill his sensual desires. The League manages to foil Morgaine's attempt to steal the stone from him and lock it up in the Watchtower. However, the Martian Manhunter's earlier attempt to locate Morgaine through telepathy is having unintended consequences: she's now in his head, giving him visions of his family back on Mars.
J'onn J'onzz gets so seduced by this vision that he tries to bring the stone to Morgaine himself, on the belief that she can use it to restore Mars. After a massive battle with the other members of the League, he's on the verge of giving it to her. But as he fights Jason/Etrigan he telepathically sees Morgaine's past betrayal, and destroys the stone instead. Despite this last-minute redemption, he's so ashamed of himself that he resigns from the Justice League. However, Jason Blood tells him that his other half misjudged his strength of character, and implores him to stay. He laments that he is still cursed, and wanders in search of atonement for his sin.
Tropes:
- Absurdly Sharp Blade: In one scene, Mordred plays with his sword by slicing entire suits of armor in half — lengthwise.
- All Your Base Are Belong to Us: The story begins with Morgaine's demonic troops capturing King Arthur's castle. Later the same troops attack the Watchtower, but this is really a distraction so that J'onn can escape with the stone.
- Anti-Hero: Etrigan. A demon thwarts an evil sorceress' plot to restore Camelot and Take Over the World.
- Apologetic Attacker: Wonder Woman apologizes in advance to the transformed Harv before she starts slugging him.
- Arbitrary Skepticism: Batman dismisses Jason's claim about Morgaine as "impossible." Jason responds "You of all people should know better."
- The Atoner: Jason does genuinely want to make up for his betrayal.
- Art Evolution: Jason Blood and Etrigan's character models have been redesigned from their preceding appearance in TNBA's "The Demon Within".
- Bittersweet Ending: The stone is destroyed, but Morgaine escapes and Jason is still cursed.
- Creepy Child: Hello, Mordred.
- Creepy Good: Etrigan. Flash and Wonder Woman, who both work with Batman, comment over how unsettling his presence is.
- Cutting the Knot: After all the fighting over possession of the stone, J'onn decides to just crush the darn thing.
- Distracted by the Sexy: At Hickman's party, Flash wanders off to chat up two bikini-clad girls while Wonder Woman interrogates Hickman.
- Dramatic Irony: J’onn says that Batman can’t possibly know what it feels like to lose his family.
- Face–Heel Turn: J'onn eventually sides with Morgaine when she promises to restore Mars in exchange for his help. He switches back just in time, though.
- Fangs Are Evil: Morgaine has venomous fangs, as we see in the first scene.
- Forced Transformation: Harv gets turned into a huge worm-like monster courtesy of Morgan. It wears off, but not before his house is destroyed as a result.
- Glamour Failure: Morgaine can see through J'onn's disguises, perhaps because of their psychic contact.
- Halloween Episode: The adventure occurs on Halloween. The Justice League doesn't care one way or the other about this, but they do pass through a costume party, and Morgaine calls on the power of "All Hallows Eve" for a spell at one point.
- I Read It for the Articles: Flash's excuse for being a fan of Hickman's magazines; clearly not believed by Wonder Woman.
- Idiot Ball: Okay, Flash is the Fastest Man Alive, and Etrigan tells Wonder Woman, not Flash, to flee with the Stone?
- Jerkass Has a Point: Etrigan chews out the League for their continued trust and allegiance with J'onn after he says to them that the latter has been compromised by Morgaine le Fay for so much as contacting her (even telepathically). After an assault on the Watchtower, J'onn leaves with the stone. Considering he was on the other end of this a thousand years before as a human (that is to say he did the betraying for her...which resulted in Camelot's collapse), you can see where he's coming from.
- Life Drinker: Morgaine to her victims, inflicting Rapid Aging on them.
- Lotus-Eater Machine: Morgaine entices J'onn with an illusion where he thinks he's back home with his (dead) family on Mars. He's almost convinced to stay until he's violently pulled out of it by Etrigan.
- Mistaken for an Imposter: When Wonder Woman and Flash try to get into Hickman's Halloween party to find the stone, the bouncers assume that they're just more people in costume.
- More Teeth than the Osmond Family: Morgaine briefly turns Hickman into a giant lamprey-like monster with no face except a very toothy mouth.
- Mugging the Monster A security guard tries to force Wonder Woman back into the queue, and gets tossed across the front lawn for his trouble. He then makes the even smarter decision of getting backup against WW and the Flash. Fortunately, Hickman (attracted to Wonder Woman) stops the whole thing from getting out of hand and personally escorts her in, with Flash running beside them. (Of course, Hickman might qualify too, trying to make a pass at her...)
- Mythology Gag: A party attendee dressed (badly) as Batman is dancing the "Batusi".
- No Celebrities Were Harmed: Aside from the artifact collection, Hickman is a clone of Hugh Hefner; same hair, same jacket, same initials (Harvey Hickman), he's a magazine publisher, and his mansion even has a grotto.
- The Punishment: Merlin's curse makes Jason immortal, and gives him access to demonic powers.
- Rapid Aging: Morgaine can age people by decades in just a few seconds. Without a steady stream of victims, she seems to revert to her true age.
- Regretful Traitor: Both Jason and J'onn. At the end, Jason regrets how hard he's been on J'onn given the similarity of their positions. J'onn, meanwhile, is so guilty about the whole affair that he attempts to quit the League, even though he did the right thing in the end.
- Rewarded as a Traitor Deserves: Jason greets Morgaine as he lets her army into Camelot. She rewards him with a venomous kiss that apparently would have killed him if Merlin hadn't intervened to give him a more lasting punishment.
- Sequel Episode: A very loose one to TNBA's "The Demon Within", picking up Etrigan's storyline and revealing more of his backstory.
- Shout-Out: Many of the attendees happened to be dressed like some of Jack Kirby's creations such as the Forever People. Fitting given Etrigan's guest appearance.
- Split Personality: Etrigan is more of a Jerkass and blunt than his human half, Jason Blood. Though he is a demon.
- Vain Sorceress: Morgaine le Fay doesn't really need to absorb the life-force of people to make spells, but doing so does rejuvenate her youth. That said, in modern times, she's always wearing a mask veil, so she's not that vain.
- With Great Power Comes Great Perks: Wonder Woman questions Hickman's use of the stone:Wonder Woman: You used the most powerful object in the world to get money and women?
Hickman: What else is there? - You Have No Idea Who You're Dealing With: Morgaine le Fay notices J'onn trying to read her mind, but she derides him to Morded as "a mere amateur", and uses his quote before trapping the Martian in a psychic illusion of him back on Mars with his family.
- Your Costume Needs Work: Wonder Woman and the Flash are initially denied entry into Hickman's mansion during his Halloween party. Wonder Woman telling a security guard, "We're the Justice League", only draws a sarcastic "Yeah. So are they." from the guard as he points to a row of (badly-dressed) row of attendees.
