It was just another day in the Badlands. RED and BLU were fighting to capture all the points, as always. Bullets and rockets flew, bombs exploded, and mercenaries dropped left and right. The central control point changed hands every other minute, the team in control being dependent on who was alive and who was waiting to respawn. The timer was constantly being reset, and the teams were in a perpetual stalemate.

That was when the RED Heavy noticed a BLU Scout sitting on a crate, facing away from him. An idler, possibly, but he needed to get him away from the control point before he returned from daydream land. Scouts were expert point cappers, after all.
He walked closer to the BLU, Sasha at ready, so when he DID attack, it would do more damage. The faster he killed the Scout, the better.
However, just as he was about to open fire, his target spun around. The last thing he saw before being knocked out was a BLU Scout wearing RED accessories.

"Guys, guys, guys! We have a problem!"
The RED Scout rushed into his team's base. His teammates looked up.
"That Scout's back!" he continued. "He's running around, doing his thing!"
The members of RED looked at one another, groaning. They called him "Rogue Scout." He had no team loyalties, going for anyone and everyone who was too slow or unaware to get away. He never killed his targets, but did something that was even more annoying: he knocked them out, taking anything of value they happened to have on them. RED and BLU stopped the fighting, as they did every time the delinquent made his appearance. After all, they had a common enemy.

Members from both teams sat down and discussed a way to stop Rogue Scout, but they had already tried everything they could think of. Attacking from behind was futile-he seemed to have eyes on the back of his head. Sentry guns never attacked him unless their Engineer had a Wrangler, and the Scout had a nasty habit of using those to turn Sentries against their teams. They even tried putting an attractive lady Spy on RED for the day. Much to everyone's surprise, he barely flinched when he saw her. He didn't even try to flirt with her for a second!
"Well, I guess we're out of ideas," the RED Soldier said. "There's no stopping that freak."
"You just don't know what'll do the trick," a girl said. Looking around the room, the mercenaries realized that they somehow overlooked the BLU Scout, a new recruit and the only girl in the room.
"I suppose you think you can do better," a Spy growled.
"Yeah, I do. You just watch."
The Scout left the room, taking only two things with her: an empty milk bottle and a can of Bonk.

"This time, STAY DOWN! I'm not wasting my energy to knock you senseless again!"
Rogue Scout lay a RED Engineer out on the ground. This run wasn't a very good one, but at least he was having fun. He looked around. The rest were probably hiding away in the bases again. No matter. He'd just break in and knock out everyone, maybe swipe a hat or two to sell later. He needed SOMETHING worth selling.
Suddenly, he noticed something flying towards him, but it was too late to dodge. It landed at its feet, shattering. It was one of those milk bottles that Scouts sometimes carried around as makeshift grenades.
The glass itself didn't hurt him, as it wasn't supposed to. But the liquid was blue, sweet-smelling, and... pain-inducing?
It could only be Bonk! But how did they know?!
He collapsed, his entire body feeling as if on fire. The sensation made it impossible to fight back as mercenaries surrounded him...

"Who woulda thought?" the BLU Engineer noted while going through the bag the delinquent carried. "The freak's allergic to Bonk!"
Rogue Scout opened his eyes. The pain was mostly gone, but that didn't change the fact he was tied up and unsure how he was going to get himself out of this mess. Nor did it change the fact his cover was blown. He reminded himself that all Scouts looked the same, so maybe he could pass himself off as someone else.

But it seemed unlikely, considering one of the BLU mercenaries just so happened to be his twin sister.