Comic Title: Action Comics #287
Publisher: DC (National Periodical Publications, Inc.)
Address: 575 Lexington Avenue, New York, NY
Cover Date: April 1962
On Sale Date: February 27, 1962 Newsstand Date February 27, 1962
Source: House Ad, Superboy #96, Page 30

Copyright Date February 27, 1962
Source: Library of Congress, Periodicals 1962

Frequency: Monthly
Cover Price: $0.12
Page Count: 32
Editor: Mort Weisinger

Title: "Supergirl's Greatest Challenge"
Pages: 14

Feature(s):
Supergirl (of Earth-1)

Writer: Jerry Siegel
Artist: Jim Mooney

Reprinted In:
Action Comics #373 (1969)
Adventure Comics #496 (1983)
Legion of Super-Heroes Archives Vol. 1 HC (1991)
Showcase Presents:Legion of Super-Heroes Vol. 1 TPB (2007)
Showcase Presents Supergirl Vol. 2 TPB (2009)
Supergirl:The Silver Age Omnibus Vol. 1 HC (2016)
Legion of Super-Heroes:The Silver Age Omnibus Vol. 1 HC (2017)
Supergirl:The Silver Age Vol. 2 TPB (2018)
Legion of Super-Heroes:The Silver Age Vol. 1 TPB (2018)

Feature Character(s)

• Supergirl (last appearance in Superman's Pal, Jimmy Olsen #60; next appearance in Superman's Girl Friend, Lois Lane #33)

Guest Star(s)

• Legion of Super-Heroes (last appearance in Adventure Comics #301; next appearance in Superboy #98)
• Cosmic Boy (last appearance in Adventure Comics #301; next appearance in Superboy #98)
• Saturn Girl (last appearance in Adventure Comics #301; next appearance in Superboy #98)
• Lightning Lad (mistakenly called Lightning Boy in this story; last appearance in Adventure Comics #301; next appearance in Superboy #98)
• Triplicate Girl (last appearance in Adventure Comics #301; next appearance in Superman #156)
• Bouncing Boy (last appearance in Adventure Comics #301; next appearance in Superman #156)
• Chameleon Boy (last appearance in Adventure Comics #301; next appearance in Superman #156)
• Brainiac 5 (last appearance in Superman #152; next appearance in Superman #156)
• Sun Boy (last appearance in Adventure Comics #301; next appearance in Adventure Comics #300)

Supporting Character(s)

• Fred Danvers (last appearance in Superman #152; next appearance in Action Comics #288)
• Edna Danvers (last appearance in Superman #152; next appearance in Action Comics #288)
• Streaky (last appearance in Superman's Pal, Jimmy Olsen #60; next appearance in Superman #154)

Villain(s)

• Positive Man and Negative Creature (no further appearances)
• The Chameleon Men (no further appearances)

Guest Appearance(s)

• Lois Lane (last appearance in Superman's Pal, Jimmy Olsen #60; next appearance in Superman #153)

Other Character(s)

• Robot thieves and an unnamed masked thief (no further appearances)
• Whizzy (a 30th century descendant of Streaky; no further appearances)
• Members of the Midvale Chapter of the Superman Fan Club (Margie and Ethel named; no further appearances)
• Three forest rangers (Joe named; no further appearances)
• Lon Duryal (chief scientist at the Android Factory; no further appearances)
• Tree-Men (creatures of planet Arbro; no further appearances)
• Citizens of 30th century Metropolis (no further appearances)

Cameo Appearance(s)

• Superman (in pictures and statuettes)

Comments:
The Legion is incorrectly said to exist in the 21st century in this story.

The Science Police are called the Earth Police in this story.

Positive Man and Negative Creature may have been hurled into another dimension, but certainly are not destroyed when they vanish in this story, since Supergirl would never deliberately destroy life.

Supergirl incorrectly assumes that no inhabitants remain in the Phantom Zone in the Legion’s era in this story. Actually, Mon-El still remains in the Zone, as seen in the first story of Adventure Comics #300, as does "the Mighty Gazor," as revealed in the first story of Adventure Comics #323. Due to the vastness of the Phantom Zone, however, Supergirl does not encounter any of its remaining inhabitants, and leaps to an incorrect conclusion.

Following this story, Phantom Girl presents Supergirl with a commemorative Supergirl statuette in the second story of Action Comics #290.

Synopsis:
The Legion of Super-Heroes summons Supergirl to defeat the Positive Man, a once-human changed into a massive destructive force by the explosion of his home planet. As they watch from their spaceship, the Maid of Might lures a Negative Creature, created by the same explosion, toward the Positive Man, and the resulting explosion causes both to vanish.

Upon returning to Earth, the Legionnaires learn that this explosion has also erased their powers. Supergirl decides to stay with them, and, working behind the scenes with Whizzy, the telepathic descendant of Streaky (aka Super-Cat), helps the Legion deceive criminals into thinking that they still possess their abilities.

However, the real reason that the Legionnaires are powerless is that they are actually members of an alien chameleon-like race who, in the aftermath of the positive-negative explosion, imprisoned the real Super-Heroes and took their places. Having fooled Supergirl and Whizzy, they project them into the Phantom Zone.

From here, the phantom heroes mentally command a scientist at an android factory to construct a bogus chameleon man, who infiltrates the Legion imposters and releases Supergirl and Whizzy from the Zone. Supergirl captures the aliens and rescues the real Legion.