A college Physics professor, Al Pratt, is set up on a blind date, by his married friend, Betty Roberts. Roberts, and her husband, drive Pratt out to the Thayer mansion, in the swanky section of Calvin City. Upon meeting his date, Marion Thayer, Pratt is aghast to discover that she is a woman in her late 50's/early 60's. Taken aback by Pratt's obvious shock at her appearance, Thayer glances at herself in the mirror, and is, herself, horrified to see her aged face. A scream from Roberts, draws Pratt's eyes away from Thayer. Roberts, too, has suddenly grown old. Pratt's keen hearing detects a strange electrical sound, emanating from another room in the Thayer mansion. Pratt decides to investigate, in his guise as the Atom. He spies two men cutting into the wall safe with laser weapons. The Atom leaps into battle, easily defeating the two would-be thieves. Confiscating one of the laser guns, Pratt returns to his laboratory, at Calvin College, to study the weapon. He discovers that there is no correlation between the gun and the aging effects. Pratt brings the weapon to a local police precinct. There he overhears a desk sergeant taking in multiple calls, from women who have all, too, mysteriously aged. Pratt decides to journey to "Earth 1", a parallel world to his own. As events on both worlds happen with a great degree of similarity, Pratt hopes to arrive before the onset of the aging effect there, and possibly ferret out the root cause of it.
Meanwhile, on "Earth 1", that world's Atom, noted physicist Ray Palmer, is in the process of taking down a quartet of thieves. As the last crook falls, Palmer is suddenly unaware of why he'd been fighting the men. He has no recollection of his identity as the Atom, and is mystified at the costume he's wearing. Moreso by his diminutive size. Palmer races back to his home, hoping he can determine some way to return himself to normal size, before his date that night, with Jean Loring. Palmer finds Pratt, in his Atom costume, waiting at home for him.. Palmer has no memory of ever meeting Pratt. Listening to Palmer's tale of the past hour, Pratt determines that Palmer has lost his memories of the last decade. Pratt shows Palmer how to work the size controls, in his gloves, to return to his normal height. Thanking Pratt, an obviously younger Palmer rushes off for his date with Loring. Upon arrival, Palmer is, at first, pleasantly surprised at Loring's amorous familiarity with him, then shocked at her talk of marriage on their first date. Loring is confused by Palmer's behavior. After all this isn't their first date. They're actually engaged to be married. As the Atom, Prat arrives and explains the situation to Loring. Pratt then takes hold of Palmer and returns them both to Pratt's world, "Earth 2".
On "Earth 2", Palmer's memories instantly return to him. However, much to Pratt's surprise, Palmer viciously attacks him. The two battle for several moments Pratt grabs Palmer, preparing to use the vibratory device to return them to Palmer's world, "Earth 1". Palmer shrinks out of Pratt's grip, grabbing Pratt's fingers as he does so, keeping Pratt from activating the device. Pratt hurls himself at the ground, hoping the sudden impact with the flagstones will jostle the device enough to activate it. The two heroes do vanish, but they do not return to "Earth 1", instead appearing on an inter-dimensional world. One that that lies in-between the two Atom's respective Earths. Palmer continues to aggressively attack Pratt. Despite being entangled in the clutching tendrils of a carnivorous alien plant, Palmer's mind stays focused on assaulting Pratt. Realizing that Palmer's life is endangered by the plant, Pratt activates the size control mechanism in Palmer's glove to return him to normal size. Without the advantage his size and mass controls give him, Palmer is easily defeated by the scrappier Pratt. Pratt finally gets them back to "Earth 1". Upon arrival, Palmer's age regresses another decade, rendering him an impetuous 14 year old boy. Palmer races off to Mount Ivy, to attend a Scienceers meeting. Palmer runs across a radio telescope, sitting atop Mount Ivy. Still overly aggressive, Palmer begins smashing the radio telescope with a large rock. With the telescope destroyed, Palmer returns to normal, though no longer having memories of anything that occurred since he foiled the robbery. A wild-eyed scientist suddenly appears, demanding to know who destroyed his radio telescope. It was picking up a new form of radiation from a distant star, which he had been studying. Pratt surmises that the radiation was from a newly born star, and that the youthful energy of that fresh celestial body, deflected by the Van Allen Radiation Belt into Ivy Town, had caused the men to de-age. Pratt was unaffected by the radiation on "Earth 1" due to his exposure to the countering radiation on "Earth 2". Pratt determine that there must be a parallel radio telescope, sitting atop Mount Calvin, on "Earth 2". The radiation it's collecting would have to be coming from a dead star, thus accelerating the women's ages on his world. The two Atoms return to "Earth 2", and race to destroy the parallel radio telescope. The radiation, however, has formed an impenetrable force field around the radio telescope. With all his might, Pratt hurls Palmer into the field. Palmer shrinks to microscopic size as he hits the barrier, slipping through it's molecules, to reach the other side. Palmer flips a switch to turn the radio telescope off, at which point, Pratt destroys it. Pratt resumes his date with Marion Thayer, while Palmer returns to "Earth 1", and, more importantly, Jean Loring.