On a barren landscape next to a mountain, an older balding man in a prisoner's uniform and nullification collar walks up to a younger man, who is working on a large capsule. The younger man says that everything is going fine but warns the capsule only sits one.
At Mount Justice, Robin and Beast Boy arrive as Nightwing reviews the Krolotean data downloaded from the computer at Malina Island. According to the files, the Kroloteans were experimenting on abducted humans for something concerning a "meta-gene." They're interrupted when the computer detects an incoming energy impulse. A capsule materializes out of thin air and the young man emerges, wearing a costume. Nightwing tells the computer to seal the cave and the young man, hearing them discuss the energy impulse, decides to call himself "Impulse." He calls all three Young Justice members by name and then goes superspeeding around the cave, investigating anything that catches his interest. Beast Boy and Robin try to restrain him and distract him long enough for Nightwing to stun and restrain him.
In Tibet, Cheshire has found a temple that she tells Red Arrow contains Roy Harper, the human used to clone her husband. She has her daughter Lian with them and tells Red Arrow that they need to rescue Roy so that he can be free of the guilt and raise their daughter properly.
Impulse tells the three heroes that he's Bart Allen, a tourist from the future and the grandson of Barry Allen, the Flash. Nightwing offers him a glass of water and Impulse realizes that the hero is trying to get a DNA sample. He obligingly spits into the glass and calls Nightwing and the others by their real names. He insists that proves he's from the future but admits that he can't tell them anything about their futures without altering history. When Mal Duncan arrives via the outside door, Impulse frees himself and runs off. Beast Boy goes after him while Nightwing tells Robin that he put a subcutaneous tracker in the water and that they can trace Impulse as he heads to Central City. When they see where he's going, Nightwing calls an old friend.
In Central City, Barry Allen and his wife Iris throw an anniversary party for their friends, Jay Garrick and his wife Joan. Barry receives a call just as Impulse arrives, says that he's Barry's grandson, and hugs him. Barry insists that he doesn't have children, and Iris reluctantly tells her husband that she just learned that she was pregnant. Impulse tells them that they're having twins, much to their surprise, and then realizes that he's giving away the future. Wally West, Kid Flash, arrives, and explains what has happened. Iris gets a call and Impulse tries to stop her from taking it, but she learns that her boss at the news station wants her to cover a new supervillain who is attacking the downtown area and plans to kill the Flash.
Downtown, the new villain releases blasts of nuclear energy, destroying a statue of the Flash.
Barry puts on his Flash costume and leaves, ignoring Impulse's suggestion that he let the Flash handle the new villain. Flash is downtown in a flash and rescues the pedestrians, and then goes after the villain. Impulse rescues him with a wind funnel and refers to the villain as Neutron. The elder speedster examines Neutron and realizes that he's giving off continuous waves of energy, making it impossible for them to approach him at any speed.
The heroes are unaware that two Kroloteans are at a nearby warehouse, monitoring their "experiment."
In Tibet, Red Arrow and Cheshire enter the temple and subdue the guards, but are soon surrounded by several dozen more.
Kid Flash arrives to help Flash and Impulse, and Flash suggests that they use Impulse's wind funnel trick to send Neutron into the upper atmosphere where he'll be harmless. They start circling him at superspeed but he increases his energy output. The Kroloteans, monitoring Neutron, realize that he's generating nuclear energy faster than he can control it.
Neutron overloads, releasing a blast of energy that destroys several square blocks of Central City. The faster Impulse and Flash carry Kid Flash to safety, and Kid Flash uses his goggles to check on Neutron. He's surprised to discover that Neutron is generating his own body, but the villain has no idea who he is. Meanwhile, the Kroloteans realize that the explosion destroyed Neutron's suit, which they were using to monitor and contain his abilities. They destroy their control device and abandon the warehouse.
Kid Flash realizes that Neutron will explode again, more powerful than ever without the containment suit. Flash uses his protégé's goggles and confirms with his superspeed vision that without the suit there are now microscopic gaps in the energy waves being released. He tells the other two speedsters that he'll run in at near-lightspeed and carry Neutron out into the desert where he can detonate harmlessly. He speeds in before Impulse can stop him, so the younger speedster goes after him, and "accidentally" trips him. Neutron detonates and Kid Flash and Jay speed in and get their friends out just in time. Once clear of the danger zone, Jay explains that he decided to put on his old costume as the Golden Age Flash to help out. Kid Flash accuses Impulse of endangering Flash, but Flash admits that he would have died if Impulse hadn't interfered. While they talk, Impulse speeds in and attaches a small blue capsule to Neutron as he regenerates again. This time when he reforms, his body is back to normal. The other three speedsters arrive and Impulse simply says that Neutron ran out of energy.
Cheshire and Red Arrow take out the rest of the guards and finds a locked room. Inside is the cryogenic unit holding Roy Harper and they free him, discovering that his right arm is missing.
The speedsters go to Mount Justice and Nightwing confirms that Impulse is both related to Barry Allen and a time traveler. Impulse says that he has to go and Barry thanks him for coming. However, when Impulse tries to activate the time-travel capsule, he discovers that it doesn't work. He admits that he doesn't know how to fix it, meaning that he's trapped in the present.
Forty Years in the Future
On a barren landscape next to the ruins of Mount Justice, an older Neutron walks up to Bart, who is working on the time-travel capsule. Bart says that the capsule only sits one, and Neutron warns him that it will burn out after a single trip. Bart knows that he'll be trapped in the past, but figures that it's better than being stuck in their desolate future. Neutron gives Bart the blue capsule to depower him, but warns that it will take more than curing him and saving Barry to prevent their future from occurring. Bart departs in the capsule and Neutron suddenly discovers that he isn't wearing a prisoner's uniform or the nullification collar. However, the rest of the world remains unchanged, even though the changes to history should have been instantaneously. Neutron realizes that Bart has somehow failed to change their past and prevent the destruction in the future.
Bart Allen first appeared in Flash (Vol. 2) #92 (June 1994) and was created by Mark Waid and Mike Wieringo. Born in the 30th century, Bart was the son of Don Allen, one of the Tornado Twins. Thanks to the intricacies of time travel, Bart is also the grandson of Barry Allen, the 20th century superhero. On his mother's side he is related to Professor Zoom and the second Captain Boomerang. Bart was born with superspeed abilities and an accelerated metabolism, and was physically age 12 after two years. He was raised in a virtual reality environment to stabilize his metabolism and was eventually cured. Bart made his way to the 20th century and was raised by several speedsters. He later joined Young Justice and then the Teen Titans, and took on the role of first Kid Flash and then the Flash during his career.
Nathaniel Tryon first appeared in Action Comics #525 (November 1981) and was created by Marv Wolfman and Joe Station. A petty thug who was caught in the meltdown of a nuclear reactor, Tryon was transformed into nuclear energy. After seeking revenge on the people responsible for the accident, Tryon took the name Neutron and began a life of crime. He often battled Superman but also joined the Fearsome Five and hires himself out as a mercenary for various criminal enterprises. In the comics his body is made entirely of nuclear energy and he has enhanced strength, invulnerability, fight, and the ability to absorb and project radiation.
The Flash (Golden Age)
The Golden Age Flash first appeared in Flash Comics #1 (January 1940) and was created by Gardner Fox and Harry Lampert. College student Jay Garrick gained the ability to move at super speed by inadvertently breathing heavy water fumes. As a founding member of the Justice Society, he battled such villains as Shade, the Thinker, the Icicle, and Ragdoll.