The Second Supergirl!
In science class at Midvale Orphanage, Supergirl gets the idea that somewhere in the universe, there may be a planet like Earth containing a double of every person, including Supergirl. She asks Superman for help to find such a planet. Superman plugs data into his Super-Univac computer and discovers the planet Terra, which orbits the star Sun-X45-266. Supergirl hopes to go there, where she may openly reveal her existence, so that she can prove to Superman she's ready to be revealed to the people of Earth.
She goes to Terra, where she discovers that the planet is much the same, but with a number of minor differences. The Supergirl she meets, Mighty Maid, operates in the open while this world's Superman, Mighty Man, must operate in secret until he proves himself.
When a disaster in space occurs, the Fortress of Marvels comes crashing down to Terra, and Marvel Man fails to catch it because he was exposed to diamond, his weakness.
The Supergirl of Two Worlds!
Supergirl and Marvel Man rush to repair the Fortress of Marvels before Marvel Girl returns to Terra. After they succeed, Marvel Girl returns and congratulates Supergirl on a job well done. She then goes to Earth to tell Superman that Supergirl is ready to be revealed to the world.
She tells the story of Supergirl's adventures on Terra, and then returns to Terra. There, she reveals Marvel Man's identity to the world. Supergirl stays for the ceremony, then returns to Earth. Superman tells her that she messed up by not checking up on Terran culture when she arrived there. Consequently he decides she's not ready to be revealed to the world.
- Supergirl/Linda Lee/Kara Zor-El
- Superman/Clark Kent/Kal-El
- Marvel Maid/Lea Lindy
- Marvel Man/Ken Clark