A/N In typical Glee style this does not really fit with the time line, but just go with the idea that Sectionals came after Karofsky was expelled but before Kurt transferred. Compared to Finn helping Puck to pass an exam, it is not a lot to ask!
Karofsky is probably OOC, but he is desperate and has passed the line of normal behaviour, even for McKinley.
Mention of NCIS, but knowledge of the programme is not needed.

Disclaimer-I own an idea but not much else.

It was early as New Directions gathered sleepily in the choir room.
Only Rachel was showing any enthusiasm, but even that was only a fraction of her usual pre-competition hyperactivity and tempered by a clear sense of injustice. For once, her attitude was warranted, as they had been denied access to the auditorium prior to Sectionals.
"...and it's our auditorium, after all. How can I be at the peak of my performance when Principal Figgins decides to hold a careers fair, of all things, the week before a competition? We need to make sure you all know how to show me to best advantage and some people," if looks could kill Finn would be performing as a corpse, "need all the time they can get on a stage to get the choreography right."
"Leave him alone, Rachel, it was just the once and it's not as if the rest of us have never been trodden on by Finn. It's almost a right of passage to become a member of New Directions. 'Squashed feet? You're in,'could be Mr Schue's catch phrase." Kurt frowned, "I actually think a careers fair is a good idea, given that the average jock around here will end up working in a car wash."
Puck shifted in his seat and told himself that it had nothing to do with the other boy's seemingly automatic defence of Finn or his views on his classmates.
"But why now and why in our auditorium?"
Santana smirked,"Because there was a whole heap of money going from some scheme to help disadvantaged youth, but it had to be available to all the kids in the district and it was about to be snapped up. So, the faculty came up with this careers thing and invited all the schools in the district, knowing that most of the kids won't bother to come. Only Coach Sylvester managed to link it to some other thing about cheerleading raising aspirations, believe it or not, and it was suddenly serious and needed more space."
Kurt shook his head," And, let me guess, the Cheerios also get money out of it."
"Of course. I'm not sure how much, but I had to move away from the staff room window at that point."
Nobody even bothered to comment on Santana's methods of information gathering. If nothing else, they were always well informed.
Finn was not particularly interested in the careers fair, but at least the subject was better than Rachel listing all his shortcomings, so he decided to keep the topic going.
"Is Scary Sue the reason why we have all these strange people coming to talk?"
"Yes, she said she worked undercover for a while and that's how she knew someone NCIS, but the Moscow State Circus beats me."
Rachel had been ignored for too long for anyone to be surprised to hear her redirect the conversation back to her concerns.
"I don't care why they're here, the point is that they are using my, um, our stage and we need it to practice for Sectionals."
"And Rachel's ego needs the space," muttered Puck, just loudly enough to be heard.
And he was not pleased to see the smile on Kurt's face at his quip. Well, only as pleased as he was to hear Tina's quiet chuckle, he assured himself. People smiling was meant to make you feel good, to feel as if it had been worth getting up so early, to feel as if the sun had shone just for you. Oh, er, in a very general, not person specific way, anyone's smile not just...quick think of something else!
"So are we gonna practice now we're here? Cos I got some Cheerios to do before class and I need to actually turn up to History or Mr Black will flunk me and I'll be off the team."
Kurt grimaced, "Charming. Still, I suppose you don't need to learn too many social niceties if you're going to clean pools for the rest of your life. The careers fair will be wasted on you."
Puck turned towards the door to hide his expression. What did they say about words not hurting? He was a stud and he did not need anyone's approval of his lifestyle. But the hard knot in his stomach told a different story.
Mr Schuester's arrival gave the class a focus and they all settled down in their seats to talk through the arrangements for Sectionals.
Puck wondered if his eyes had a life of their own as he caught himself watching Kurt again. The other boy was sat almost diagonally opposite, on the front row with Mercedes, and it was easy to look bored whilst keeping him in view.
Puck had had a lot of practice lately and the compulsion to follow Kurt's every movement did not seem to be going away any time soon. It had taken a while for Puck to realise he was doing it and he refused to put a name to anything.
When he told himself it had started out of concern when they found out about Karofsky's bullying, he focussed on the protective instinct, told himself that he would protect any of his choir mates and ignored the way even a smile could lighten up his day.
When Kurt had grabbed his hand in excitement the other day, he had not spent the rest of lunch with his fingers curled tight as if to keep that brief touch intact. Or spent hours contemplating how to recreate that ecstatic look that had made his stomach do loops. It was difficult to see how he could do anything to equal the bully getting expelled.
He had also wasted a lot of time contemplating quite how bad things had got for Kurt if his reaction was so uncontrolled that he actually touched another boy. It did not take Puck's current level of surveillance to notice how careful he was around his own gender, especially when you saw his open and tactile way with the girls. He had snatched his hand away when he realised what he had done and luckily, or was it unluckily, before Puck had got over his shock and grasped those fingers back. All because David was gone, so what had David done? Something more than slushies and locker checks, which only seemed to increase Kurt's scorn for the jocks rather than make him afraid. Puck shook himself and realised that Mr Schue was getting ready to start the practice. As he lifted his eyes from Kurt's profile, which seemed to have magnetic properties, he saw an unwelcome but familiar face at the door and tensed.
David Karofsky stormed into the choir room with no ceremony and a gun.
In any other circumstances, it would have been funny how in tune the New Directions were, as they gasped in unison with the door slamming shut.
Mr Schue stood awkwardly, "Now, David, you really shouldn't be here and especially not..."
"Shut up."
Given that the gun was waved wildly in his direction, nobody could blame the teacher for sitting down quickly and, more importantly, quietly.
Puck watched the weapon turn back to the students and its target seemed clear to him.
Before the others had even reached the same conclusion, Noah Puckerman was planted firmly between the gun and Kurt.
"Puck, get out of my way." The surprise had left a slight quaver in the intruder's voice but his arm was steady.
"No."
"This has nothing to do with you."
Puck snorted, " Did you really think you could walk in here waving that and we would all just let you?"
"The others have."
"They just aren't used to guns. I've seen enough, I live in a crappy neighbourhood. You don't scare me, Karofsky."
"I don't care about you. If you get in my way that's your problem. I want him." It did not need the head jerk to know who 'him' was. But something in the way it was said caught Puck's attention.
"Why?"
"He got me expelled, my parents aren't talking to me, they're even talking about some boarding school for troubled teens."
"But that's not it, is it?"
Kurt stood, "Puck, just move away." His voice was calm, but the resignation was clear and triggered something in his protector.
"Do you see what you've done, Karofsky? I don't know what you did, but it must have been bad. And now you want to hurt him again." He turned his head a fraction towards Kurt, but kept his eyes firmly on the danger in front. "You don't deserve this, Kurt, and he's going to have to go through me to get anywhere near you."
There was an echo this time as two voices said,"Why?"
Puck looked at David thoughtfully.
"For the same reason you came here, I think, but while you want to hurt him, I want to protect him."
Karofsky looked startled and glared at the boy in front of him.
"You?" he said with scorn. "The McKinley stud."
Puck's mouth twisted and he let out a laugh that was anything but amused. " Just when you thought life really sucked it screws you over again."
"He won't want you, thinks he's too good for any of us."
" He is. He'll get out of this cow town, go and be fabulous on Broadway or something and forget all about us."
" But he's mine."
" God, Karofsky, what century are you in? You can't just say 'I want', people choose to be with someone. Did you really think Kurt would want you? Have you seen him? Always primped up to the nines, wearing stuff that costs more than my whole wardrobe and probably yours too. And we haven't exactly treated him well. Dumpster dives and slushy facials are hardly a good replacement for flowers and chocolate. Man, even I know he's the type to want to be courted."
" But he was mine and then he ran away." David's voice had quietened and there was a hint of uncertainty in it.
Puck's already tense stance tightened even more and his voice, though not raised, had an almost threatening note. " What? What did you do to him?"
Kurt tried to push past his bodyguard, but Puck only blocked the move, keeping himself firmly between the boy and his attacker.
" Noah, please."
"No way."
" But I don't want you to get hurt. Let me just talk to him," he swallowed nervously and Puck could tell that he was trying to put on a good front, but was petrified.
" Kurt, he came in and pointed a gun at you. I think we've gone past you two talking."
Karofsky edged forward. " If you just come with me, Kurt, no-one will get hurt. I love you and you're mine."
Puck felt the shiver run through the body behind him and spoke before the countertenor could decide to sacrifice himself.
" You don't point a gun at someone you love. Look, I understand it's frustrating to love somebody who doesn't love you back, but you can't force them."
" What do you know? You're only stood there cos you think you're so badass that I won't shoot you."
" You pointed a gun at the person you say you love. I know you could shoot me, but you know what, Karofsky, I'm still stood here. Because I would rather it were me than him."
" What you think you've a chance? You were in charge of dumpster dives. You're no better than me. But at least he kissed me."
Puck felt another shiver but it did not need that for him to know the truth.
"No way would he kiss you voluntarily. You mean you kissed him and that's why he ran."
" But he gave me this wedding cake thing."
" You took it, it was for my Dad and Carol, you..." Kurt surged forward but only succeeded in plastering himself to Puck's back. He stepped away and took a deep breath. " I'm sorry, David, but Noah's right. There's too much history between us. It's flattering, I suppose, but I just don't feel the same."
Even with a gun pointed straight at him, for a minute Puck could only focus on those words. They applied to him almost as much as Karofsky and hearing that sweet voice actually saying it out loud was like a knife in the gut. Obviously, however much he had denied his feelings and known there was no chance of reciprocation, some part of him had held onto a shred of hope.
The silence stretched until David raised his eyes and saw Puck's expression.
"You meant it," he whispered. "I would have to kill you to get to him. Oh, God, what have a done?"
Without warning a tormented wail left Karofsky's throat as he slid slowly to the floor.
Kurt made to approach him, but was blocked again.
" He's still got a gun." Puck edged closer to the figure rocking on the ground. " David, give me the gun."
Eyes looked blearily at him. " I did it all wrong, didn't I? I'll end up at that awful school and you get to be his hero."
" So he's nice to me for a bit for all the wrong reasons, it doesn't change anything." Puck shrugged." You and I are stuck here, Lima Losers. Just give me the gun and maybe we can sort this out without you going to that school. Either way, it's gotta be better than juvie and that's the alternative."
For what seemed an eon, Karofsky held the gun still pointed at Puck before lowering his hand and dropping the weapon on the floor. Puck kicked it away as the door flew open and two armed men burst in.
Puck almost laughed when Mr. Schuester finally decided to speak. Now the man remembered he was meant to be in charge. Behind him he could hear Kurt's harsh breathing and, with a last glance to check on Karofsky's position, he turned and enveloped the other boy in his arms. Kurt collapsed against him shaking as the strangers introduced themselves.
" Special Agent Gibbs, NCIS. Here for the careers nonsense. And that's McGee, securing the firearm. Can anyone give me a quick version of events while we wait for local forces?"
Most of the class groaned to themselves when Rachel stood up and started speaking, the rest were not so restrained.
" My name is Rachel Berry and you might want to remember that as I will be famous..."
Special Agent Gibbs interrupted with little ceremony," The quick version, I said. Can anyone manage that?"
Surprisingly, it was Tina who spoke up.
" David Karofsky, the one on the floor, was expelled recently for threatening Kurt, the one in the stripy pants. We were about to start practicing, we're a show choir, when Karofsky burst in here with the gun and aimed it at Kurt."
She paused and the students all held their breath waiting to se how much she would reveal.
"To be honest, we were all too stunned to do anything. I've never seen anyone actually pointing a gun like that, but Puck, that's Noah Puckerman, with the Mohawk, lives in a, well, a..."
" Tell it like it is, Tina, I live in a crappy area and it's not the first time I've seen a gun pulled on someone."
" Alright, so, as he says, Puck was able to react quickest and he got between Karofsky and Kurt. Karofsky seems to think Kurt belongs to him, just because he wants him to. I mean, he said he loves Kurt, but it doesn't sound like love to me, more an obsession. Anyway, Puck sympathised with him, you know, saying he understood and persuaded him that pointing a gun at someone was not right and not the way to show your love. So Karofsky dropped the gun on the floor and Puck kicked it over to Mr. Schue as you came in."
"Thank you, Tina, wasn't it? Very succinct. So are they?" Gibbs jerked his head towards the Kurt who was still held securely inPuck's arms.
" No, but I think Kurt was more frightened than he seemed and he tried to get past Puck to stop him getting hurt and Kurt's a crier, so.."
Gibbs grimaced," So it's better to leave him to calm down?"
"Yes. The minute his Dad hears about this, he'll be here, but once Kurt gets it out of his system he'll be able to answer any questions and calm his father down."
Gibbs sighed and looked around the room.
" McGee, take this lot and find a room to wait in," he gestured at the students still sat in silence. " The teacher, too," he added, barely glancing in that direction. It sounded as if the man had been of little help. " He can stay with them and you can bring the local police back, assuming that the principal managed to call them."
By the time McGee had assembled everyone and left, Kurt had stopped crying and was sat down trying to repair the damage to his appearance. Puck was sat next to him, but neither had said a word in the interim. Karofsky was still on the floor, now shaking uncontrollably.
Gibbs took a chair and placed it in front of the two seated boys.
"OK. So what do you want the story to be?"
Kurt looked indignant as Puck looked away silently.
"Tina told you what happened."
"Why did he," the gesture took in the crumpled figure on the floor," think you, what was the phrase, ah, yes, ' belonged to him'?"
"Because he's a mixed up jerk and, look, I don't know, he threatened to kill me, that's why he was expelled."
Puck looked up, " He's always been a bully, not that I can talk, but when I came back it seemed to have got worse, especially to Kurt. The guys tried to get him to back off and I would've helped but.."
"You couldn't risk it Puck." He turned to the agent,"I suppose I ought to tell you that Karofsky kissed me. He was being his usual Neanderthal self and I just snapped. I followed into the locker room and asked him why he kept picking on me and," there was an audible swallow," and he just kissed me. I pushed him away, but after that, well, it got more scary, when he pushed me into lockers it was harder but also..."
"Sexual?"
"Yes, more body contact and he looked at me, well, that scared me more than anything. Then he made a rude gesture when he saw Finn and I practicing dancing for our parents' wedding, only Dad saw and Finn made me tell him about the bullying. I never mentioned the kiss, I don't believe in outing anybody, it was only," his arm waved around the room, " that anyone found out about that. So, I did say that he had threatened to kill me and Dad went to the principal and he was expelled. But, I never did anything to make him think..." Kurt's voice quavered and Puck put his arm back around the slighter boy, glaring at Gibbs.
"He had no reason to think...Kurt has always made his disdain for us jocks perfectly clear, it's not like..."
As Kurt shushed the other boy, Gibbs wondered if he was the only one to catch the hint of bitterness in that voice.
At that point McGee returned with a police officer and the adults stepped to one side to confer, but Gibbs made a point of watching the two boys out of the corner of his eye, as two more officers took Karosky off.
The local representatives of the law made it abundantly clear that, whilst they appreciated the assistance so far, they had no further need of NCIS's expertise and they were free to leave as soon as possible.
McGee shook his head," Well, I know it's not exactly complicated so they should manage from here,but a 'thank you' might've been nice."
Gibbs smirked," More complex than they'll work out, but nothing illegal."
He took in his colleague's face and frowned slightly.
" Come on, McGee, surely you spotted the anomaly? The story was good, but maybe too good."
McGee hesitated and Gibbs would swear he could see their entire encounter with the group run through his mind. When the younger man turned to face the lines of chairs he was too quick to see the look of approval on his boss' face.
" He, Puck that girl said, he was sat up there on the end, the gunman came in the door closest to his intended victim. There was a teacher present, although to be honest he struck me as more frightened than the kids, and all the others were closer, including I gather a strapping great quarterback soon-to-be stepbrother. Yet Puck was out of his chair and in front of the target before any of them moved. So, either Puck was expecting it, but none of the others were concerned about leaving them together, or Puck had a reason to react without thinking. The whole used to guns bit doesn't totally explain it."
" Better, McGee. Having spoken to them I think Puck moved on instinct, to protect."
" Why not just tell us if he and Kurt ..."
" Because they're not. My guess is that Kurt was as shocked by the conversation and what it revealed as by the gun pointed at him. Interesting that he turned to Puck though."
"Maybe not, the stepbrother was a bit awkward about another boy wanting Kurt, I doubt he would be happy cuddling. The other boys were OK, but friendly rather than close and the girls seemed more used to histrionics from Kurt than tears."
"Yes, I got the distinct impression that there is a lot hidden there. One way to do it."
" We can't all carry off the dark and brooding."
Gibbs narrowed his eyes at his subordinate, but was met with a clear, guileless look that only Tim could get away with.
" Well, we need to get back to this careers farce and telling the wrong people about what we do. Seems the Glee club has more subtlety than the rest of the school put together. See if you can speak to that Tina again before we leave, she spun an excellent cover story with just enough truth to fool most people. I like her, she's got potential."
Neither man commented on the fact that two of the boys at the centre of the recent drama were leaving by the other door, hands 'accidentally' brushing against each other.