And now for something completely different. The scene is a post-apocalyptic world. Devastation and destruction cover the land. We see two people, an older man with a teen who is about to execute a mission, and the youngster knows this is a one way trip.
Flash to our heroes inside Mount Justice, Nightwing, Robin, and Beast Boy are discussing their latest mission plans, when the alarm sounds and a temporal rift opens in front of them. A machine emerges as the rift closes. Out of the machine is the teenager we just saw in the previous scene, who is an impulsive, fast-talking, fast-acting teenage superpowered human. He reveals that he is a speedster, and knows the identities of everyone in the room and reveals them, to the dismay of Nightwing. They try to subdue him, but even after capture, the self-dubbed Impulse frees himself and takes off in search of his ancestors.
As one family is about to learn of its offspring, another family tries to close the door on its past. Red Arrow and Cheshire, with their child in tow infiltrate a League of Shadows base, where Cheshire is certain the real Roy Harper is being held. Their stealth tactics fail when their child laughs after they down two guards, and instantly the troubled couple are surrounded.
Barry Allen, the Flash, gets a phone call while he and Iris are at the home of Jay and Joan Garrick. The call is too late as Impulse arrives and immediately proclaims he is the grandson of Barry. Wally West arrives as confusion reigns the room. The confusion is clarified as Iris tells Barry she is expecting, but Bart Allen aka Impulse drops the bomb that she is carrying twins, something Iris did not yet know. The uncomfortable family party is broken as a villain, Neutron, emerges and Barry, Wally, and Bart rush out to confront the menace.
We cut back to the base where we find the unconscious bodies of numerous members of the League of Shadows. They come to a room with a capsule resembling the one holding Conner Kent, and finally, Red Arrow can put his obsession to rest as they uncover the real Roy Harper, missing arm and all. When questioned why the Justice League did not know about his location, Cheshire tells Red Arrow that she has connections where the League does not.
In Central City, Neutron is giving the speedster heroes a run for their money, as they are unable to put down the fiery menace. At one point, he lay defeated but some unknown power allows him to reassemble himself, flesh, bone, and metal and continue the attack. We then learn some aliens, unknown as they remain hidden in the shadows for now, are controlling the antagonist. Finally, the Flashes are able to concoct a plan to sap his power and defeat him. During the recovery, we see Bart/Impulse place a blue micropill on the human inside Neutron which seems to eradicate any trace of his unknown source of powers.
We then rewind back to the scene where Bart is about to leave on his time travel journey, and now we know the man with him was Neutron. As Bart vanishes on his one-way trip, the uniform on the once-Neutron changes, and he believes that Bart was successful on his mission and time has changed.
Sadly, he looks around to see, that in fact, nothing has changed at all, and forty years in the future, something goes horribly wrong, leaving Earth a scorched wasteland.
This episode was different from previous ones, in the area where we are abruptly introduced to Bart Allen who joins the speedsters as Impulse, and we get a fast resolution to the whereabouts of the real Roy Harper. The episode felt short and not as in-depth as others, but still delivered and as usual, answers questions while asking even more.