Terminate Dave Katz.
Five’s next assignment came from a nearby vending machine in downtown London; where he had just completed his latest mission with the utmost efficiency. He tucked the transmission into his suit pocket, retrieved his rifle and picked up his briefcase to set the date and time. Five had been a time-traveling assassin for three years now and only had two more years left until he could retire and avert the apocalypse. The fact that he would be reunited with his family and see them for the first time in over four decades was beside the matter, what was important was that he completed his mission.
There was a telltale flash of blue as he was transported to the edge of the battlefield. Five dove to his stomach to avoid the bullets flying above him and aimed his rifle towards two soldiers, one of which he knew was Dave. There was no way to tell which was which by appearances alone, but Five had too shoot one soon or he would be spotted, and everything he had worked so hard for would go up in flames.
Five was about to say screw it, and try to get a closer look, when he heard the soldier on the left say the name Dave. The voice sounded strangely familiar, but Five had no time for such things, he had to get back to his time and prevent the apocalypse. He wished this wasn’t the way to do that, but it was the only way until he solved the equation. He swiftly adjusted his rifle and fired. The last thing he heard as he time-traveled away from Vietnam was the soldier on the left shouting “Christ on a cracker! That was a close one, huh, Dave?”
Something about that phrase bothered him that he could never figure out, it was always at the edge of his minds grasp. No matter, his cause was too important to get hung up on the familiarity of a voice and a phrase. Five repeated this to himself as the solution hit him like a ton of bricks, as he solved the equation, the way to travel back and prevent the apocalypse. Dropping his gun, he flipped open Vanya’ book and quickly to double check his math; which he finally had correct. Not looking back, Five ditched the Commission, opened a portal to his past and jumped through it in order to save the world.
When Five followed the trail of bloody footprints from a bathroom to Klaus’s room, saw his tattoo and dogtags, he didn’t make the connection; after all, how Klaus time-traveled was far more important than when. The setback that the loss of the briefcase caused was another distraction. A third distraction was fooling the Handler so he could steal information about the apocalypse from her. Then Five and his siblings had to find Harold Jenkins, then they had to stop Vanya from ending the world, when that had failed, he had to time-travel them all to safety and a fresh start. Overall, there was not a lot of time to contemplate one of his old assignments.
It finally clicked when him and his siblings arrived in the past in their teenage bodies, all seven of them.
“Christ on a cracker! Ben you’re alive!” Klaus gleefully tackled Ben into a hug while Allison, Luther, and Diego expressed similar sentiments.
Reeling from his revelation, and noticing they were back in the mansion, Five teleported to his room to process everything. The clues had been right in front of him, he’d just been too blind to see what they spelled out. The Handler must have known what she was doing when she sent him to Vietnam, but Dave’s death wasn’t her revenge, Five realized, that was about the time stream. Klaus wasn’t supposed to appear in 1968, She had Dave killed to make Klaus return to 2019. Her revenge was that she could have sent any agent to kill him, but she sent Five. Dave and Klaus must have been close enough that his death empowered him to get sober; not even Ben’s death had done that. The Handler had once again succeeded in separating Five from his family. Not with distance this time, but with a secret Five could never tell. Five killed Dave.