Appearing in "Crisis on Earth-One!"
- Justice League of America
- Justice Society of America
- Crime Champions
- Snapper Carr (Mentioned only)
- Doctor Mid-Nite (Charles McNider) (Mentioned only)
- The Sandman (Wesley Dodds) (Mentioned only)
- Starman (Ted Knight) (Mentioned only)
- Wonder Woman (Diana Prince of Earth-Two) (Mentioned only)
- Vandal Savage (Mentioned only)
- Interdimensional Limbo
- Amulet of Anubis
- Cloak of Destiny
- Crystal Ball of Merlin
- Fiddler's Fiddle
- Fiddler's portable vibrator
- Green Lantern Ring
- Helmet of Fate
- Icicle's Cold Gun
- Green Kryptonite
- Lasso of Truth
- Nth Metal Wings
- Philosopher's Stone
- Anesthetic Arrow
- Micro Arrow
- Paint Arrow
- Stun Arrow
Synopsis for "Crisis on Earth-One!"
Batman chairs a meeting of the Justice League of America. He tells the team that he just learned that Chronos, Doctor Alchemy and Felix Faust have banded together as the Crime Champions and intend to commit three crimes simultaneously. The group splits into three teams to take down each of the super-villains.
Meanwhile, on the parallel world of Earth-Two, the Justice Society of America have received a challenge from three of their most well-known adversaries: The Fiddler, the Icicle and the Wizard. Eager to begin adventuring as a team once again, the JSA officially come out of retirement.
Back on Earth-One, Felix Faust plunders a sunken battleship. Aquaman, the Atom and Martian Manhunter arrive to stop him, but Faust crushes Aquaman with a tidal wave and conjures fire to keep the Manhunter at bay. The Atom knocks the fire away, and Martian Manhunter uses his Martian-Breath to blow the Atom like a bullet towards Faust, but the villain suddenly disappears.
Elsewhere, Doctor Alchemy uses his Philosopher's Stone to rob an armored car, giving it wings. Superman and the Flash arrive to stop him, but the Flash mysteriously begins vibrating and disappears. Doctor Alchemy uses his power to turn a nearby fire hydrant and power line pole into Green Kryptonite, which slows Superman down. Green Arrow tries to stop the villain with his trick arrows but is caught in glue and his arrows are turned to weeds. Finally he uses arrows equipped with lead paint to cover the Kryptonite hydrant enabling Superman to free him and they go after Alchemy, but he manages to escape.
In Powers City, Chronos the Time-Thief robs a vault. Batman, Green Lantern and Wonder Woman show up and Chronos clips Batman's Batrope with a crystal watch disc. He keeps Green Lantern at bay with a blast of yellow smoke from his Flying Sundial and he manages to elude Wonder Woman's golden lasso with hands fired from a watch. Wonder Woman saves Green Lantern by lassoing him from the smoke, he catches Batman. Like the other villains, Chronos mysteriously disappears.
The three Earth-One villains reappear at a secret lair between Earth-One and Earth-Two where they meet up with the Fiddler, the Icicle and the Wizard. The Earth-Two villains regale their Earth-One partners with stories of how they recently defeated the Justice Society. The villains decide to switch places with one another with Chronos, Doctor Alchemy and Felix Faust remaining on Earth-Two, and the Fiddler, Icicle and Wizard migrating to Earth-One.
When the Earth-Two villains arrive on Earth-One, they disguise themselves as their partners so as to confuse the members of the Justice League. The Wizard uses his magic to complete their disguises, he becomes Alchemy, Icicle becomes Chronos, and Fiddler becomes Faust, and they begin a crime spree at the gambling district known as Casino Town. The Justice League tries to fight them, but their unfamiliarity with these Earth-Two villains gives the criminals a distinctive edge in combat. Superman's vulnerability against magic enables the Wizard to spring a final trap against the group. The criminals manage to apprehend the League and imprison them inside their own Secret Sanctuary. None of their powers are strong enough for them to break free. Worse, the Flash still appears to be missing in action.
With little recourse, the League uses the Crystal Ball of Merlin to contact the Flash. The Flash tells them that he is trapped between dimensions and that they should use the Crystal Ball to contact their Earth-Two counterparts the Justice Society. The League conducts a séance over the Crystal Ball and the orb's magic succeeds in bringing the Justice Society to Earth-One. Both teams pledge to help the other in stopping the Crime Champions.
- This story continues next issue.
- Reprinted in DC 100-Page Super Spectacular #6, The Greatest Team-Up Stories Ever Told, Justice League of America Archives, Volume 3, Crisis on Multiple Earths Vol. 1, DC 100-Page Super Spectacular DC-6 Replica Edition, Showcase Presents: Justice League of America Vol. 2, Justice League of America Omnibus, Volume 1 and Justice Society of America: A Celebration of 75 Years.
- This issue features the first team-up between the Golden Age Justice Society of America and the Silver Age Justice League of America, both of which are the creations of writer Gardner Fox. This begins a series of annual team-ups between both groups which continues until Justice League of America #245. This story also expands upon the concept of the Multiverse - an ever-evolving plane of parallel dimensions where each reality contains a planet Earth, but with vast differences between them. The concept of the Multiverse was first introduced in Flash (Volume 1) #123 in a story called "The Flash of Two Worlds". In that story, Barry Allen, the Flash of mainstream Silver Age continuity traveled to the dimensional home of Jay Garrick, the Flash of Golden Age continuity. It is not until this issue that the individual dimensions are provided with name designations. The reality corresponding to Jay Garrick and the rest of the Justice Society is established as Earth-Two, whereas the reality of the Justice League is known as Earth-One.
- The absence of Snapper Carr is explained when Green Arrow reveals that he is away at college finishing his final exams.
- Hal Jordan meets Alan Scott for the first time. They will team-up in Green Lantern Vol 2 40.
- Ray Palmer meets Al Pratt for the first time. They will team-up in The Atom Vol 1 29.
- Secret Origins (Volume 2) #50 homages an illustration of the first encounter between the JLA and JSA in this issue. However, there is a small rearrangement of the position and presence of characters: Absent: Dr. Fate, Wonder Woman (who had not came to Man's World in this point of time) and Superman (who wasn't JLA's active member in Post-Crisis); Present: the two Flashes, the two Black Canaries (instead only one) and Dr. Mid-Nite; Kept: Green Arrow (bearded instead), Batman, Martian Manhunter, Golden Age Hawkman, Hourman, the Green Lanterns and the Atoms. It is not clear whether the adventure against the Crime Champions is valid in the Post-Crisis, but surely happened no dimensional travel.
- Batman becomes the chairman of the Justice League in this issue.
- It is revealed that the Fiddler is actually bald in this issue and wears a wig to disguise his features.
- An homage to the cover of this issue would be used in Alan Moore's Image Comics series Supreme. This comic within a comic was The Allies #21, wherein the Allies meet their WWII counterparts, the Allied Superman of America.
- Discuss Justice League of America Vol 1 21 on the forums
- Cover gallery for the Justice League of America series
- Images from Justice League of America Vol 1 21
- Justice League Recommended Reading
- Justice League of America (Volume 1)
- Justice League of America (Volume 2)
- Justice League of America (Volume 3)
- Justice League of America (Volume 4)
- Justice League of America (Volume 5)
- JLA (Volume 1)
- Justice League (Volume 1)
- Justice League (Volume 2)
- Justice League (Volume 3)
- Justice League (Volume 4)
- Justice League International (Volume 1)
- Justice League International (Volume 2)
- Justice League International (Volume 3)
- Justice League Europe (Volume 1)
- Justice League America (Volume 1)
- Justice League Task Force (Volume 1)
- Justice League Quarterly (Volume 1)
- Justice League Dark (Volume 1)
- Justice League Dark (Volume 2)
- Extreme Justice (Volume 1)
- Justice League Elite (Volume 1)