The Six Red "K" Perils of Supergirl! is a 1962 two-part Supergirl story, which continues into the next issue's story, The Strange Bodies of Supergirl!.
Since Mr. Mxyzptlk has restored her powers and made her invulnerable to Kryptonite, Kara assumes she's also invulnerable to Red Kryptonite. In space, she discovers six Red K meteoroids and fuses them together into one, destroying them. But since Mxyztplk had imagined Green Kryptonite when he gave that command, she is in fact not invulnerable. As there were 6 different meteoroids, she will experience 6 different effects.
When she attends the local fair with Dick Malverine, the symptoms of the Red K begin to manifest themselves. First, she becomes incredibly fat and puffy, and she's forced to pose as one of the balloon floats. Next, she becomes a wolf-girl, and inspires a movie producer about to kill himself.
Finally going home, she checks in on Dick with her supervision to discover that his father's dying of a rare disease. She then also begins to shrink due to Red K, as the third effect. This gives her an idea.
Flying to the hospital, she flies inside Mr. Malverine's body and physically attacks all the virulent bacteria inside. Before the red K wears off, she flees and returns home to await the next strange effect of the Red K.
The next Red K effect, which she discovers while visiting the fair again the next day, is that Supergirl literally grows a second head. The second head has a separate consciousness and knows how to speak, but has no memories and no idea who she is. Supergirl explains everything, dubbing the second head as "Supergirl Head No. 2".
Despite Supergirl's objections, the second head insists upon seeing the fair, and Supergirl agrees. They walk out of the bathroom and explore the fair, making no effort to conceal their appearance. They are asked to become a sideshow act but angrily decline. The two actually begin to have fun together, and the second head helps Supergirl save a falling plane. However, this effect soon wears off, and as she vanishes, the second head begs Supergirl to save her. Before the Girl of Steel can do anything, though, her second head disappears. Supergirl laments the loss, feeling like she'd had a sister.
The next effect is an extended hallucination, in which she causes the deaths of everyone around her by developing a new power called Fatal Vision, which kills anything it touches, even Krypto. She flees the Earth in this hallucination, and uses her power to instead kill members of an evil alien race who slaughter their neighbors. It's soon revealed that none of this ever actually happened.
The final effect is that she temporarily becomes a mermaid, dubbing herself Super-Mermaid. She decides to use the time to visit her other boyfriend, Jerro. By this time, Lenora, the sister of Lori Lemaris, has fallen in love with Jerro and has been shielding her thoughts so he wouldn't find out. When Supergirl resumes her romance with him, Lenora becomes jealous and depressed, and blunders into the Valley of the Hands. Meanwhile, Jerro proposes marriage to Supergirl, who is hesitant. Jerro reads in her mind that she also has feelings for Dick Malverine, but tries to persuade her anyway.
Supergirl and Jerro must rescue Lenora from the Valley of the Hands once she has been captured. Afterwards, she returns to the surface to meet Superman, who has returned from his visit to the 31st Century and the Legion of Super-Heroes. He informs her that he has decided to reveal her existence to the world.
- Supergirl/Linda Lee Danvers/Kara Zor-El
- Mr. and Mrs. Danvers
- Dick Malverine
- Supergirl Head No. 2
- Lenora Lemaris