Twin black holes pulsate within a binary star system. On patrol in Chicago, Supergirl spies a trio of joyriders, swerving in traffic. Supergirl prevents their car from crashing, then hauls the lot of them to the nearest police precinct. In Metropolis. at the Daily Planet, Perry White, Lois Lane and Jimmy Olsen discuss the looming crisis, while Clark Kent stares out the window. Kent spots the double black holes, with his super-vision, and decides to investigate, as Superman. Supergirl, as Linda Danvers, receives a phone call from Barbara Gordon, asking to meet in Gotham City. Danvers, as Supergirl, immediately flies to Gotham City to speak with Gordon, who has assumed her guise as Batgirl. The looming crisis has terrified Batgirl to her core. Supergirl does her best to ally her friend's fears, but is interrupted by a the sight of a small plane, breaking up in the sky. Supergirl flies off to rescue the pilot, before his plane falls into the wave of anti-matter consuming the world. Supergirl meets up with Superman. The two fly off to the Rennial V sector of space, to investigate the twin black holes. Superman notices that Supergirl is unusually pensive, but the Maid of Steel offers no answers for her mood.
Superman and Supergirl pull back from the twin black holes, as their combined energies impossibly pool between the cosmic phenomena. The black holes' energies coalesce into the form of Supergirl's old nemesis, Blackstarr. It is then that Supergirl remembers that she had triumphed over Blackstarr, in their last encounter, by tricking her into moving in between twin black holes, an act which seemingly destroyed Blackstarr. Supergirl suffers a barrage of quasars at Blackstarr's hands. Superman attacks from the rear, but Blackstarr repels the Man of Steel with a massive gravity wave. Immobilizing Supergirl with the formation of four black holes around her limbs, Blackstarr moves in for the kill. Supergirl steels herself for the killing blow, while pleading with Blackstarr to forego her destruction of the universe. At Supergirl's words, Blackstarr suddenly become aware of the looming crisis jeopardizing the very universe, a crisis Supergirl erroneously believes Blackstarr responsible for creating. To save the universe, Blackstarr shelves her plans for vengeance against Supergirl, in favor of an alliance. In sync with the very universe itself, Blackstarr determines that Superman is the root cause of the crisis. Supergirl gets Balckstarr to stay her hand against Superman, long enough for Supergirl to speak with the Man of Steel.
Supergirl attempts to convince Superman to leave the universe, to prove to Blackstarr that his presence has nothing to do with the crisis. Superman refuses, believing that Blackstarr is merely trying to separate them, the better to destroy Supergirl. Superman presses the attack against Blackstarr, only to find Supergirl intervening on Blackstarr's behalf. The two Kryptonians scuffle briefly, until Superman fends Supergirl off with his heat vision. Superman again closes on Blackstarr. The cosmic villainess slows time around Superman, drawing him into another black hole. Supergirl slams into the Man of Steel at maximum velocity, hurtling them both into the black hole. Their momentum carries them out to the other side, where they find themselves in virtually the same space they just left. Blackstarr realizes her error, determining that the universe is actually shrinking. With Superman flying in one direction, and Supergirl the opposite, Blackstarr links them both to her considerable cosmic energies, and re-expands the entire universe. While this has not ended the coming crisis, it has, at the very least, been considerably slowed. Superman and Supergirl rendezvous with one another, and find that Blackstarr has disappeared. Whether intentionally or not is unknown. Despite their stopgap measures, Supergirl can't shake her sense of impending doom.