Underworld Unleashed was a three issue limited series published on a bi-weekly shipping schedule from November to December of 1995. All three issues were collected as a trade paperback in 1998. The series was written by Mark Waid, with illustrations by Howard Porter, and inked by Dan Green and Dennis Janke. Editorial credits include Ruben Diaz, Alisande Morales (assistants) and Brian Augustyn. Accompanying the mini-series were four one-shot specials, which featured various DCU characters and expanded upon events taking place within the main series. (See Recommended Reading section)
The Rogues Gallery undertake a strange mission under the urging of Abra Kadabra. Given little explanation, they agree to strike at five specific though seemingly unremarkable locations across the United States. Each attack is committed simultaneously yielding explosive results far beyond their expectations. Each of the Rogues is consumed by raging green fire as their respective target sites go up in flames.
The incident does not go unnoticed by the super-hero community. In the Justice League satellite, the League members take note of the attacks and spring into action. Flash orders Blue Devil to call for back up as they leave him on the station. Blue Devil is the only one to realize the strategic pattern of the five random locations. By tracing a line between each site, Blue Devil draws a perfect pentacle. He knows that something has been set free.
In Keystone City, the Trickster is frustrated with the pedestrian pranks that he has been reduced to just to make ends meet. When he reads about the tragic fate of the Rogues, he grows depressed knowing that his fellow villains never rated higher than petty crooks. Trickster decides that he wants to go for the "big score".
At Belle Reve Penitentiary, a convict named Lou goes to the office of the prison's chaplain. He complains that a guard named Finney swiped his Betty Grable calendar, and the man behind the desk agrees to help Lou out. He provides Lou with a riot shotgun and tells him that Finney will be in the turbine room at precisely midnight. Lou doesn’t trust the "chaplain", but he accepts the weapon and agrees to carry out his vengeance at mid-nite. After Lou leaves, the man withdraws the missing Betty Grable calendar from behind his desk.
At midnight, Lou ventures down to the turbine room. He finds Finney and viciously guns him down. The gunfire sets off sparks that damages the turbines. Engineers races about to correct the situation, but there is nothing they can do. The power shuts down and the doors to the prison cells unlock. Dozens of super-powered criminals escape out into the night.
Back in Keystone, the Trickster allies himself with another old Flash foe – the Rainbow Raider. The Raider shows him a tapered candle with intricate carvings on the side. He tells Trickster that someone had delivered it to him, but he has no idea who or why. Before the evening ends, the Trickster surreptitiously pockets the candle and replaces it with a rubber chicken.
When he lights the candle, he finds himself instantly transported to an unknown location. The Trickster gapes in surprise as he finds himself in the company of dozens of super-criminals, many of whom are likewise in possession of a green, lighted candle.
A demonic being known as Neron steps out and introduces himself. He takes credit for staging the Belle Reve breakout and for providing the villains with their respective candles. In exchange for their souls, Neron promises each of them their fondest desire. Many of the villains are only too happy to accept Neron's offer. Some even feel that their soul belongs to him already. Others, such as the Joker, are present just for the sheer thrill of it. Some however, have little desire to play second fiddle Neron. Mongul for one, refuses to acknowledge Neron's power and attempts to strike him. Neron effortlessly punches Mongul to the floor, then stomps on him with his boot. Trickster debates the value of accepting Neron's offer. He then remembers that he wanted to "take the next big score" and thinks, "It doesn't come bigger than this".
There is one more guest who arrives after receiving a special invitation – Blue Devil. Blue Devil steps out from a spiraling green haze of smoke and addresses Neron.
Blue Devil agrees to accept a mission on behalf of Neron. He knows that making a deal with the Devil is a poor decision, but Neron only asks him to destroy an abandoned power station. Blue Devil scopes out the territory and makes certain that no innocents will be harmed by his actions. He strikes his trident upon the ground, and a rippling wave of energy emerges, consuming the power station.
Meanwhile in Hell, Neron sets a welcome table for those villains who agreed to serve him; namely, Lex Luthor, Doctor Polaris, Circe and the Joker. Neron finds the Trickster scurrying about behind the others and pulls him out into the open. Trickster really has no idea why he is even bothering to listen to the arch-demon. Neron leaves, and the other villains have fun tormenting the Trickster, especially the Joker. Convinced that he knows the source of Neron's power, they interrogate him further, until the Trickster reveals that Neron's power is contained within his soul jar. The villains begin conspiring to steal Neron’s power for themselves.
Meanwhile in St. Louis, the Flash races about the city putting out fires. Neron appears before him and makes him an offer. In exchange for his soul, he will grant his fondest desire – the return of his mentor Barry Allen. An image of Barry flickers in front of the Flash's eyes, but the hero knows better than to make deals with demons. He refuses the offer and runs off.
Later, Neron appears inside the Batcave. He addresses Batman and makes a similar offer. The visage of Batman's deceased former protégé Jason Todd walks up to greet him. Batman is haunted by the image, but staunchly turns down Neron's offer.
Neron appears next in Honolulu, Hawaii where he approaches Superboy. He offers Superboy the chance to become what he’s always dreamed of – Superman. Like the others, Superboy turns down the offer.
There are some heroes however, who actually accept the demon's deal. Hawkman, Ray, Triumph and the Spectre agree to sacrifice their eternal souls in exchange for their deepest desires.
In California, movie producer Marla Bloom flies across a remote bluff in the hopes of capturing some ideal stock footage. Her location brings her close to the power plant that Blue Devil only recently destroyed. Unable to see because of the loss of power, their helicopter collides with a power transformer and explodes. Blue Devil soon hears the news and falls into a state of shock.
In New York, Neron appears and finds Green Lantern averting a crisis in Central Park. He makes the same offer that he made to the others, in this case, to resurrect Alexandra DeWitt, but Kyle reacts violently and the two begin battling each other across Central Park. Neron gains the upper hand, but also mentions that the soul he covets most is one of purity and innocence.
Back in Hell, Luthor and the Joker come up with a plan to pierce Neron's Soul Jar. Polaris, Kadabra and Circe pool their mystical and scientific resources together and succeed in rupturing the container. As the jar is breached, a swirl of green smoke reaches outward spiriting Polaris, Kadabra and Circe away. Luthor and the Joker are not at all shocked by the spectacle. In fact, everything went exactly as they had planned. Now there is no one else to challenge their bid for power. The Trickster keeps a safe distance from them, and wanders off to come up with his own plan.
At the Justice League satellite, Flash and Green Lantern call in the reserves and tell them about their respective experiences with Neron. Kyle mentions Neron's quest for a pure soul, and the other heroes believe that he intends on capturing Superman. The Man of Steel is not present at this meeting and nobody knows where he is.
As Neron's power continues to grow, the effects of his influence have taken hold of the Earth. The entire world appears to be erupting in waves of violence and panic.
The full might of the Justice League pierces the barrier to the Underworld and confronts Neron's demonic army. Convinced that Neron has captured Superman, they navigate through the circle of Hell to find him. Neron meanwhile, sits atop his throne with Lord Satanus kneeling before him. Satanus acknowledges Neron's power, and offers up his own sister Blaze in exchange for lenience. Blaze is outraged, citing that they have no chance of overcoming Neron if their power is divided. In a moment of brief defiance, Satanus remarks that there is a single word that would give even Neron pause. Neron destroys Satanus before he has the chance to utter the word, but the Trickster, having stayed hidden behind Neron's throne, now realizes that there is in fact a way to beat the Devil.
Back on Earth, the JLA reserves conduct damage control in various cities swept in a grip of violence. Triumph, Gypsy and Mystek fight demonic gargoyles in Paris. Blue Beetle and Booster Gold try to help crowds of people consumed by a mystical hunger. In Montana, Damage, Green Arrow and Black Condor protect a National Guard armory from civilian raids. In San Francisco, the Sentinels of Magic fights off hordes of cultists and demonic agents. In Gotham City, Major Disaster causes a massive traffic jam, which enables Gorilla Grodd, Metallo and Blockbuster the chance to hijack a truck carrying nuclear weapons. Fortunately, Batman, Robin, Black Canary and Huntress arrive just in time to stop them.
Back in Hell, the heroes continue their advance against Neron's minions. Blue Devil is the first to reach him, and threatens to gain his “pound of flesh” for the inadvertent death of Marla Bloom. Neron turns Blue Devil's trident against him and the resulting energy surge appears to destroy him.
Soon after, the heroes discover that Superman is not trapped in the Underworld at all. Trickster begins to realize that Superman was never the "pure soul" that Neron sought at all. His true target was Captain Marvel. The evil influence of Hell begins to overwhelm the other heroes and they fall prey to their darkest, most base instincts. Neron manipulates them into attacking Captain Marvel, who thus far, seems unaffected by the corruptive reach of Hell. Captain Marvel tries talking to the heroes, but they keep coming after him.
Unexpectedly, Blue Devil rises from the dead – now a true devil, rather than a man trapped inside of a costume. As Blue Devil busies himself with Neron, Trickster sneaks out and approaches Captain Marvel. He tells him that Neron fears a magic word, and Marvel immediately knows what to do. He speaks the magic word "Shazam", and a powerful mystic lightning bolt erupts in Hell, freeing the other heroes from Neron's dark influence. While the heroes attack Neron, Trickster pulls Captain Marvel aside and tells him his plan. Captain Marvel offers his soul in exchange for Neron freeing the Earth and all the heroes with no other demands. Neron greedily takes Marvel's soul and makes the deal only to discover that the pure soul, offered altruistically, couldn't be retained by him as Trickster knew would be the case. Thus all the heroes and the Earth are freed with Captain Marvel retaining his soul.