The First time they ever met, John Casey already knew everything there was to know about Professor Charlie Eppes. Some whiz-kid math genius, who thought that scrawling letters and numbers all over a chalk board would get them closer to the weapons manufacturers who were hiding somewhere in South America than some leg work and a little talking.

With this in mind, he did what he always had to the whiz-kids he was bundled with (and there had been a few – something about genius didn't age well) and stood behind him to give a grunt at the painstaking work of the past few hours. It was a particularly eloquent grunt, one he'd had a lot of practise with. It said "You really think this will help us? Why not just go home, kid? You are of absolutely no use to me at all" with a side of all the intimidation a 6'6" trained assassin could. Which was quite a lot, and generally resulted in very fast transfers on their part. (Sometimes he thought the General used him as a Geek Gauntlet, a way of testing their mettle. Sometimes he thought she was testing his.)

Therefore it was some surprise when the kid showed his true colours by looking him up and down and asking, quite politely if very coldly, if he had anything to say. Using his first name was a nice touch, too. (John knew men who had the freedom to walk down Hollywood Boulevard and shoot a man in the head without an arrest warrant who were still afraid to call him anything except Captain Casey.)

After the explanation of his work (which John didn't understand) and then an analogy using the idea of rain falling on a roof (which he sort of did) he gave John a square of land to search in Peru. After about an hours search, at about the point he had almost given up and about half an hour after he started impugning everything about the kid from his family to his sexual habits, they found the place.

As he looked around at the warehouse stuffed with enough munitions to wipe out China, and again as he got his commendation and elevation to the rank of Major, John Casey thought he should probably thank the other man. (And maybe, internally, apologise for the bit in Chinese as he grabbed onto some thorns during the search. He wasn't even certain if Professor Eppes had a dog.)

The Second time they met, they had already passed the posturing stage. Mostly, anyway.

What was left was gentle sniping, John pretending to see faults in the calculations (once even being right) just to see Charlie's frenzied scurry over to the board he had pointed out, searching through the equations only to fall short, turning to John and glaring as he realised that he had been fooled. Again.

Midway, John goes out and grabs coffee for them both making sure he remembers which hand his long black is in, and which is the mess of sugar and cream that Charlie prefers. He realises with a jolt that he is pleased this man has never been in a situation where he can't trust the milk, and can't buy the sugar for love nor money. He's happy that Charlie can't remember boiling the kettle for five minutes, and while it's still disgusting, drinking it because he needs the caffeine, needs to still have the energy to complete a mission.

Charlie's clearance is as high as his, but he still knows nothing about anything. To be perfectly frank, that's how John prefers it. He likes the fact that despite his clearance and his skills, Charlie is still an innocent. (Though he tells himself he only likes the rarity of it.)

When he gets back, the coffee is luke-warm and Charlie is practically bouncing as he shows the ways this reminds him of a bonsai tree, the pieces that are clipped chosen for aesthetic appeal as well as sturdiness. He wonders if this is how Charlie thinks all the time, seeing the world as a mass of formulas making everything logical and neat.

After, he buys a bonsai. He's seen them before, and always liked them, in the time he spent in Japan. He's often thought of getting one before, so the timing of his purchase means nothing (and he will stick to that story even under torture because in some twisted way, he almost believes it himself).

The Third time they meet, John smirks and greets Charlie by his first name, and is rewarded with a beam of joy, as though he can't believe he was remembered.

Charlie is pinning up maps with red squiggles that John really hopes mean something to Charlie, because he is lost. The team he has been asked (ordered) to work with trickles in and Charlie starts to explain his working while they slouch in their chairs and stare blankly at the professor. One mutters something about how they have no time for a fucking math lesson and he is politely escorted out by Major Casey, (John ignores the little voice which reminds him of his first reaction to Charlie) returning with a bruise on his cheek and an apology for the professor.

He watches their faces and listens as they mutter over his unreasonable reliance on the work of some math guy and grins, partially because it makes half of them nearly wet themselves, and partially because he knows Charlie will be right. He knows it with the kind of certainty that he knew he should join the air force, and knew that America was his country, and knew that that one job in Prague was going to be bad news. It isn't faith. It just is.

By the time Charlie is proved right, the various agents all trickle back into his 'office' bearing coffee or doughnuts and apologetic eyes, all except some arrogant little greenhorn from the CIA who John has thought longingly of killing over several points.

He hasn't said anything out loud, so John ignores the snide looks he sends Charlie's way every so often, and instead memorises his name for his Death List (starting with his fifth grade math teacher, and running through a long and varied list of acquaintances. He has to be thankful that he's had the opportunity to remove many names from his little list, and he gets paid for it).

Bryce Larkin is not going to be forgotten.

The Fourth time they met up wasn't on a mission. Well, not a mission Charlie was supposed to know anything about.

John found out later that Charlie was lecturing at nearby Cambridge University and had somehow (he suspected a judicious mix of flattery and steamrolling all objections) been convinced to come a local pub to try English beer. That local pub happened to be where he was working undercover as Sam Bainbridge. Charlie calling out his name would therefore be very bad.

"Charlie! It's me, Sam!" He grinned down at the other man who looked confused for a moment, before finally understanding that, for tonight, he was 'Sam'.

John was prepared to come in as an old friend of Charlie's, make small talk for a few moments, then wander off. It was understandable that he was surprised when one of the nerds sitting around Charlie offered to grab him something to drink because "any friend of Professor Eppes is a friend of ours". The target wasn't there, and Charlie was looking at him hopefully, so John figured, what the hell.

"So," one of the women who had been fawning over Charlie asked, stretching the word out. "How do you two know each other?"

Charlie blushed slightly and stammered out a story about how Sam was a friend of his brother. He wasn't the worst liar John had ever met, but he was definitely in the top five. Everyone had formed their own assumptions anyway, so John casually slid his knee against Charlie and shuffled his chair closer, leaving a mixture of disappointment and happiness playing all over Charlie's little math groupies.

He found the evening surprisingly enjoyable, Charlie interrupting every time the conversation got too technical and explaining sotto voice the really geeky references (although he didn't really need it in the case of the Batman vs. Wolverine argument which he got into rather enthusiastically).

He didn't know how he found himself going back to Charlie's hotel (though it was a much nicer place than the hellhole 'Sam' was staying in) but he was glad he had.

When Charlie left a week later, John found himself giving Charlie his emergency contact number, for the phone he took with him on every mission, and promised to call the professor. (It was the first time he'd ever actually meant it when he said that, and he found himself enjoying it.)

The Fifth time they met wasn't actually the fifth time at all. John had stopped counting meetings, showing up whenever they both had time free and were in the same country.

But it was the fifth time he put a meeting on record, and in the eyes of the US government, that made it their fifth meeting. The Buymore was about a twenty minute drive from CalSci, and Charlie's work often utilised technology available at the Buymore. It would have been logical to expect Charlie's arrival, but John hadn't even thought of the possibility.

If he'd had even a little advanced warning (Chuck doing his 'deer in the headlights' impression would have done), he could have hidden, gone out to the cage or into the employee's lounge. Instead, he was standing with Grimes, barely restraining the urge to rip off Grimes' arms and beat him around the head with them (also known as just the usual chit chat) when he felt a tugging on his sleeve.

"Hi, do you know anything about sound cards?" The man who asks wouldn't get a second glance from Casey on the street, apart from the fact that he wears a shoulder holster, but standing next to Charlie means several familiar features stand out.

John stared at the man's companion. "Charlie?"

"John? I haven't seen you in ages!" He grinned happily and captured John in a hug. "And this was definitely not on my list of places to look. Larry, this is John Casey, an old friend whom I met in England. John, this is my brother Don – you remember me talking about him?"

Old friend might be Charlie's current euphemism, but Don suspected something. When the handshake came it was a touch too firm to be anything other than a warning.

John could practically see Charlie's curiosity running over as he tried to work out why an NSA agent would be working at his local Buymore, and thought to head it off early. "Why don't we grab dinner tonight?"

He could feel Grimes' surprise and turns to glare at the little monkey man with all the venom he can muster. (There isn't as much as he had hoped for, this whole mission and all the people are tainting him with their niceness.)

Charlie blushes and agrees to meet him at an Italian place near the university which apparently does great tiramisu, while Don glares, probably wishing he'd added more force to the handshake.

John knows this is all going to be a lot of trouble – Beckman will have to be told (and she'll give that look which always creeps him out because no one has ever tried to look maternally at him before) and Sarah will need to look after Chuck tonight (and that woman cannot keep it in her pants which means a love-struck Intersect again) and all that is the least of his problems right now.

The nerds are staring, like they can smell blood and have realised that he might be human and he can just see them all falling over themselves to be friendly. The thought crosses his mind that now they'll try to talk to him and touch him and invite him places. Charlie better be worth it.

As he made his way to the Weinerlicious, avoiding all Nerd or Green-Shirt contact, he had just one thought.

He was.