Shopping in a boutique for swimwear, Linda Danvers is accosted by a very pushy sales woman, who forces her to try on a pair of sun glasses. To Danvers surprise, despite her super strength, she cannot remove the sun glasses. Monitoring the whole affair from afar, two alien brothers. Out on the street, Danvers spies a malfunctioning crane, and flies into action, as Supergirl. No sooner has she resolved the situation then she receives a broadcast, through the sun glasses, compelling her to fly to Metropolis. Danvers pays a visit to her cousin, Clark Kent, requesting an impromptu lunch date. While Kent readies himself to go out, Danvers switches Kent's glasses with another pair. As soon as Kent dons the glasses he, along with Danvers, are summoned to the alien's craft, submerged under San Francisco Bay. The second Superman and Supergirl board the alien vessel, they go on the offense, destroying weapons and putting down regiments. Realizing that the command to report to the aliens was not specific enough, the elder brother, Gur, takes over the communications station and orders the two heroes to cease all movement. Enraged at his officer's oversight, Gur disintegrates the communications operator. Gur's younger, more pacifistic, brother is horrified at Gur's actions, and begins to question Gur's motivations for this conquest of Earth. He also notices that Gur has been keeping himself in isolation, more and more frequently, over the past several days.
When next Gur appears, he decides to have a bit of sport to test Supergirl's obedience to him. A subhuman captive is brought out, and Supergirl is instructed to flash freeze the hapless creature with her super breath. Supergirl blows on the creature, but nothing happens. Supergirl is then instructed to lift a gun turret, but, again her super powers fail her. Gur tires of the exercise, instead sending Superman to the Justice League satellite, with instructions to enslave the membership, with more mind control glasses. Supergirl's powers return and, with no standing order against her, she begins destroying the alien vessel, and all who oppose her. Taken aback by her sudden actions, Gur is quick to recover and orders her to cease all movement. Gur instructs his brother to give Supergirl the command to kill the subhuman creature. To spare the creature, Gur's brother orders Supergirl to use her heat vision, to burn the creature to cinders. Supergirl's heat vision melts the sun glasses controlling her, freeing her to act independently again. Once more, Supergirl tears into the aliens, before departing to stop Superman from enslaving the Justice League of America. Superman attempts to convince the Justice League members to don the glasses willingly, as they will bestow super vision to each hero. When Supergirl enters and reveals the truth, Superman angrily seizes the Atom and tries to force the glasses onto the Tiny Titan's face. As one, Batman, The Flash, Supergirl, and Aquaman grapple with the Man of Steel. Despite their best efforts to take him down, Superman still manages to deck the Green Arrow, before shrugging Supergirl and the Flash off of him. With Superman focused on putting Batman and Aquaman down, the Green Lantern is able to destroy Superman's glasses with an emerald beam.
Realizing his brother's treachery enabled Supergirl to break free from his control, Gur draws down on his brother, and begins firing wild shots at him. Gur's brother finally understands what is happening. Gur is going blind. An errant shot blasts a hole in the ship's hull, allowing the waters of the San Francisco Bay to flood the vessel. Hearing his brother sneaking up on him, Gur is able to clip him, following the sound of his movements. Gur's brother awakens on deck, to find the crew have abandoned ship. Gur was actually shot when he tried to bar the crew from escaping. Unwilling to allow Gur to die alone, his brother returns to him. Gur's brother embraces him, as both men are engulfed by the waters of the San Francisco Bay. Arriving too late to save the brothers, Superman and Supergirl repair the alien's craft, so that they may, at last, return home.