In a park at Gotham City, people run in terror as Mr. Freeze launches an attack on the citizenry. Someone throws a Batarang at him and emerges from the shadows: Robin. Mr. Freeze is unimpressed, and Batman arrives to deliver the final blow.
In Star City, another icy villain, the Icicle, is attacking a bridge when Green Arrow and Speedy attack him. Speedy stuns him and says that today is the day.
In Pearl Harbor, Killer Frost has frozen a harbor's worth of ships. As Aquaman and Aqualad attack her, Aquaman asks if his protégé is excited. Aqualad prefers to focus on the matter at hand and knocks out the villainess. Once he's done, he admits that he's excited.
In Central City, Captain Cold is fighting the Flash and Kid Flash. Kid Flash is in a hurry to wrap up the case, and disarms the villain so that Flash can knock him out. His sidekick insists that he quit stalling.
In Washington, DC, the Justice League assembles at the Hall of Justice. Kid Flash and the Flash arrive last. As the go in, the crowd takes photos and Speedy insists that they're no longer sidekicks. J'onn J'onzz and Red Tornado greet them, and inform them that they have complete access. However, the adult heroes insist on going on their own to debrief about the coincidence of four ice villains striking at the same time. Speedy objects, insisting that they're being treated as sidekicks. The others have no problem until Speedy explains that the Hall of Justice is just a relay station to the Justice League's orbital base, Watchtower. Aquaman tells him to stand down, but Speedy realizes that Green Arrow doesn't consider him as an equal and walks away.
An alarm goes off and Superman notifies the heroes that Cadmus is on fire. However, Zatara says that a villain is conducting a major operation to black out the sun. The Leaguers decide to focus on the latter, and dismiss the fire as inconsequential even though Batman admits that he's had suspicions. Once alone, Kid Flash, Aqualad, and Robin realize that the League doesn't trust them, and wonder why they didn't go with Speedy. Robin hacks the computers and checks out Cadmus, but there isn't much information. They decide to become a team and go on a mission.
At Cadmus, an explosion knocks two scientists out a window. Kid Flash rescues them while Robin swings up ahead to enter with Kid Flash. Aqualad uses his water focusing devices to rescue the scientists and teams up with the others. They catch a glimpse of someone entering an elevator, and discover it's a high-speed express elevator going into the bowels of the earth. They find a series of tunnels and Kid Flash speeds ahead. He discovers a horde of giant creatures marching by with smaller creatures riding them.
In a secret lab, Dr. Desmond is working on the Blockbuster project. The Guardian comes in and says secret he'll begin his investigation into the fire when the authorities leave, and a g-gnome reported intruders. Dr. Desmond insists that the facility is security, but the Guardian insists on investigating. He suggests that the Guardian leave his g-gnome behind, but the hero says that he has to keep it with him at all times.
The three teen heroes realize that the facility is powered by tailor-bred life forms, genomorphs, that are bred to produce power for the base. Robin checks the computers and discovers that the Cadmus scientists are breeding an army. Robin also finds a file on Project Kr. The Guardian arrives and starts to interrogate them. However, when they point out that the scientists are breeding living weapons, one of the g-gnomes concentrates and Guardian orders the other g-gnomes to attack.
While Aqualad and Kid Flash hold off the g-gnomes, Robin hacks the base security and summons an elevator. They get away just in time and head to sub-level 52, where Project Kr. Aqualad wonders if they're in over their heads, but before they can contact the League, they arrive at Sub-Level 52. One of the Cadmus' mutated scientists attacks them telekinetically, and the heroes head for Project Kr.
Kid Flash gets to the project security door as it closes. He jams the door and Robin and Aqualad get through just in time, closing the door behind them. Robin disables the door while Kid Flash finds a test chamber containing an unconscious clone of... Superman. Robin confirms that "Superboy" is a force-grown clone created from Superman's DNA. Three g-gnomes telepathically feed him an education and make him a league. They try to call the League but realize that they're too far underground.
Outside the vault, Dr. Desmond arrives and discovers that the Guardian and the others are unable to get the door open. The scientist orders the g-trolls sent in, but the Guardian warns that they don't want to get on the wrong side of the Justice League. Desmond says that they can't let the heroes escape, and tells one of the g-gnomes to telepathically contact the g-gnomes inside the vault.
The teen heroes agree to free Superboy, who immediately attacks Aqualad. The others try to restrain him, but the clone is as strong and invulnerable as Superman. Superboy finally defeats the three heroes and slams the vault open.
Robin first appeared in Detective Comics #38 (April 1940) and was created by Bob Kane, Jerry Robinson, and Bill Finger. The first Robin was Dick Grayson, a circus acrobat whose parents were killed by gangster Boss Zucco. Batman took him under his wing and adopted him as his ward while training him as a sidekick in his battle against crime. He eventually grew up and took on the identity of Nightwing. His first replacement was Jason Todd, a street orphan who tried to steal the tires from the Batmobile. He was killed by the Joker as the result of a 1-900 telephone poll held by DC Comics. He was subsequently replaced by Tim Drake, who deduced the identity of Batman and approached him about taking on the role of Robin. Batman accepted, acquiring a third partner. Other individuals to take on the role of Robin have included Stephanie Brown and Damien Wayne. Alternate versions have included Dick Grayson, the Earth-2 adult-age Robin (whose costume the adult Robin here uses), and Carrie Kelly, a 13-year-old girl who took on the role in The Dark Knight Returns.
Wally West first appeared in The Flash (vol. 1) #110 (December 1959). The nephew of Barry Allen, he suffered from the same freak accident that gives his uncle superspeed, and donned a similar costume. He joined the Teen Titans and served as his mentor's sidekick. With the death of Barry Allan, Kid Flash took on the name and costume of his uncle. Wally eventually married TV reporter Linda Park and had twin children who inherited his abilities.
The character seen here is created specifically for the series by Greg Weisman. He has since been introduced into the comics in Brightest Day #4 (June 2010), by Geoff Johns and Ivan Reis. In the comics he is Jackson Hyde, the son of Aquaman's mortal enemy Black Manta. The exact nature of his abilities is unknown as of the time this episode aired. Aqualad has hard water abilities similar to those possessed by Aquaman's wife, Mera, but has visible gills on his throat similar to those possessed by Black Manta and his henchmen, who he genetically engineered to breathe underwater.
Superboy first appeared in Adventures of Superman #500 (June 1993) and was created by Karl Kesel and Tom Grummett. After the seeming death of Superman at the hands of Doomsday, an executive director at Project Cadmus stole Superman's body and created a human clone with simulated Kryptonian abilities that he gained via telekinesis. Setting out on his own, Superboy eventually became a hero in his own right. He was adopted by Jonathan and Martha Kent and took the name "Connor Kent." Superboy is seemingly killed during the events of Infinite Crisis, but was later resurrected by the Legion of Super-Heroes.
Speedy first appeared in More Fun Comics #73 (Nov. 1941). Roy Harper, Jr., was the orphaned son of Roy Harper Sr., a forest ranger who died saving a Navajo medicine chief, Broken Bow. Broken Bow trained Roy Jr. in the use of the bow and arrow, and eventually came to the attention of wealthy millionaire Oliver Queen. He ended up helping Green Arrow against a burglar, and Queen adopted him and revealed he was actually the heroic Green Arrow. He took the name of Speedy because he beat Green Arrow to the draw and battled at his mentor's side during the Golden Age. He was later updated for the Silver Age and after serving as Green Arrow's sidekick and overcoming a drug addiction he went on to fight crime as Arsenal and later Red Arrow.
Bruce Wayne first appeared in Detective Comics #1 (May 1939) and was created by Bill Finger and Bob Kane. Young Bruce Wayne's parents are killed before his eyes by a criminal, and he vows vengeance on criminals everywhere. After years spent training himself to the peak of mental and physical excellence, Bruce witnesses a bat flying into his home and realizes he can use it as a figure to strike awe in the hearts of superstitious criminals. Since then, Batman has undergone many changes, retcons, and deaths, but has returned from each stronger and more determined than ever. As of the time this episode aired, he has appeared in one live-action TV series, several animated series, and seven live-action movies.
Aquaman first appeared during the Golden Age in 1941 in More Fun Comics #73 - created by Mort Weisinger and drawn by Paul Norris. Arthur Curry discovers he's an Atlantean and the hereditary King of the Seven Seas. He was basically an ongoing backup character and didn't even appear on a cover until 1960 (in Brave & The Bold #28, as a now-Silver Age member of the Justice League in their first appearance). He got bounced from back-up to back-up until getting a solo run in Showcase and finally got his book in 1962. He became one of the first DC characters to become a married man after appearing in the comics and then have a son. Despite his relatively lack of powers, the character has appeared in numerous TV series, including Superfriends, Challenge of the Superfriends, Superman: The Animated Series, and Smallville. The idea of an Aquaman movie is a storyline in the TV series Entourage.
Green Arrow is a Golden Age hero created by Mort Weisinger and originally drawn by George Papp (in More Fun Comics #73, November 1941). Green Arrow was a wealthy millionaire in real life, had a red-costumed sidekick (Speedy, later Arsenal, who shows up over on Teen Titans), drove around in a Arrowcar and hung out in the Arrowcave. He progressed to the Silver Age, and joined the Justice League (issue #4, April/May 1961) and when he lost his own comic book, the writers stripped him of his fortune, changed his costume, had him grow a beard, and he became a new "liberal" type of 70's hero. His appearance here reflects his Golden Age appearance in his original costume and no beard. The Earth-1 (main) Green Arrow eventually "died" and was replaced in the League by his illegitimate son Connor Hawke who took on the role of Green Arrow, but Oliver was resurrected and got a new series initially written by filmed movie director Kevin Smith.
The Silver Age Flash first appeared in Showcase #4 (October 1956) and was created by John Broome and Carmine Infantino. Police scientist Barry Allan was doused with electrified chemicals and gained accelerated speed. Inspired by the (then) comic book exploits of the Golden Age Flash, he donned a flashy costume and went out to fight crime. A charter member of the Justice League, the Flash served with distinction until he was killed in Crisis on Infinite Earths. He was eventually resurrected 20 years later and serves as the premiere Flash of the DC Universe.
Leonard "Len" Snart first appeared in Showcase #8 (June 1957) and was created by John Broome and Carmine Infantino. Snart was a small-time crook who determined that the best way to defeat the Flash was to create a weapon and charge it with particles from a cyclotron. This created a weapon capable of projecting extreme cold. Snart donned a blue-and-white parka-like costume and dubbed himself "Captain Cold." He became a charter member of the Flash's Rogues' Gallery and battled the Flash and other superheroes on many occasions. His sister, Lisa Snart, married another Flash Rogue, the Top, and for a time the two reformed and became bounty hunters. Snart has since returned to a life of crime and is a de facto leader of the current Rogues. Captain Cold has no superhuman abilities but is an expert marksman and has extensive familiarity with cryogenics. He can use his "cold gun" to fire bursts of ice, extreme cold, and generate highly elaborate cold-mirages.
Dubbilex first appeared in Superman's Pal Jimmy Olsen #136 (March 1971) and was created by Jack Kirby. Dubbilex was the DNAlien creation of one of the adult Newsboy Legion members, Dabney Donovan, while working at Project Cadmus. He served as a mentor to Superboy, and subsequently became Head of Genetics. Despite possessing vast telepathic and telekinetic abilities, he was killed by Codename: Assassin.
Jim Harper first appeared in Star-Spangled Comics #7 (April 1942) and was created by Jack Kirby and Joe Simon. Harper was a police officer who took on the costumed identify of Guardian when he had to go after crooks that the law couldn't touch. During this time, he took on guardianship of several orphan boys, who became the Newsboy Legion. In the modern day, Harper was cloned and his mind transferred into the new, younger body. He served as head of Cadmus Security, and has had several clones created since then.