And so it was John found himself sitting next to Sherlock in the front of Mycroft's car (apparently Sherlock was a bit quicker than Scotland Yard might have liked when it came to picking locks and hotwiring cars). His phone rang from his pocket. He glanced at the number and put it back with a sigh as they turned onto the next road.

"Mycroft?" John guessed.

"No, he's in a meeting. Lestrade. Probably wants me to look at some old case or something, and I can't afford the time." John nodded and looked out the window. The car was disconcertingly quiet for a few minutes until Sherlock opened the music app on his phone and handed it to John. "Pick something you like."

John scrolled through the songs and found himself staring at a screen of mostly unrecognizable characters, so he just set it to shuffle. He certainly recognized the violin tune that came up first as one that Sherlock often played when he was still up at four in the morning. "How do you have it labeled?"

"Depends on the time period. Anything written before 1900 is in Arabic. Before 1950, Russian. 1970, German. 1980, Japanese. 1990, Mandarin Chinese. 2000, French. And anything more recent than that is Gaelic."

John nodded as if he understood perfectly. "Okay. Why?"

Sherlock kept his eyes on the road in search of the next street. "After I killed Father, Mycroft and I dropped out of school. Mummy wanted to make sure we didn't stop learning altogether, so she set a competition for us to see who could learn the most languages. I spent a few hours translating all my music one Saturday and never really got around to changing it."

Neither of them said anything for a while. John wanted to say something, but didn't know how to respond to that. They both seemed perfectly content to sit and listen to the music, ranging from the violin piece that had played at first to a song by the Beetles to some sort of foreign rap. John was more than a little surprised by the variety. What Sherlock had said had reminded John of what he'd learned about the detective's childhood just the other day, though. John just didn't know if he wanted to know any more about it, for one, and he didn't know how touchy the subject was with Sherlock, for another. He spent three songs trying to put together a question about it, but couldn't find the right words. At that point, he just gave up on it for the time being, figuring that if it really mattered, the words would come to him later.

Sherlock could read John easily enough, though. "You're worried." It was a statement, not a question.

"No, I just – it's fine." John turned out to the window and tapped out the beat of the song on the armrest.

Sherlock sighed. "You're worried about me and what happened with my father."

The tapping stopped. "Okay, so I'm worried. I'm worried because I've only just learned that my best friend had an alcoholic father, and that he killed that father when he was eight. I'm worried because that happened ages ago and I only just found out about it, and it makes me wonder if there's anything else you hide because you don't want to talk about it or make people worry about you. Because you act all cold and detached and you called yourself a sociopath once, but you're not, because I know you, Sherlock – or at least I thought I did – and that's not actually you. It can't be. So, yes, I'm worried." John looked down at the floor and then back up to the window and started tapping again. "Sorry. I… I'll shut up."

Sherlock bit his lip and pretended to put all his attention on the road, even though he didn't really need to. He didn't know if he wanted to say anything or not, and either way, he didn't know what he could say.

John waited to see if Sherlock was going to say anything else, but he didn't, so he reached over and turned up the music a bit. They spent the rest of the drive listening to Sherlock's music and waiting at stoplights.

It was half past two when the gothic structures Sherlock had referred to in the book came into view. Sherlock turned onto a side street. "John, welcome to Cambridge."

They left the car behind a café near one of the libraries. Sherlock locked the doors and looked around for a moment. "Definitely the library," he said, not quite loud enough for John to think he was actually addressing anyone. He checked something on his phone and then nodded as if confirming what he'd already known. "Coming?" he asked, already making his way towards the library. John ran to catch up before falling in step with Sherlock.

Sherlock stopped in the middle of the room when they entered the building, taking in his surroundings. "Split up. You start down here, I'll take the second floor."

"Sorry, but what are we looking for, exactly?" John asked before Sherlock could run off.

"Anything that looks like it's connected to Moriarty." Sherlock took off up the stairs, two at a time, and John was on his own. He scanned the floor and saw books, lots of books, and a computer room in the back. He shrugged. She had said she was pretty good with computers, so it was a good as any a place to start, wasn't it? When he stepped into the room, though, he realized he had absolutely no idea what he was looking for. Another card? A signature? An autographed picture? A nice little note saying, "Hey, it's Moriarty, and you're three steps behind me. Hurry up," maybe?

John sighed and sat down at one of the computers. He opened the library catalogue. A show-off who's good with computers – maybe she was trying to be really obvious by changing some authors or titles. Quick searches for "Moriarty", "Mary McNaughton", and "Sherlock" didn't find anything useful, though – just a few names tucked into the middle of some novels that really did exist, according to Amazon. John reached back to adjust the monitor and found a piece of paper stuck to the side. He pulled it off and glanced it over, expecting to see someone's phone number or book list or something. It wasn't, though. It was a sketch of the same "M" that had shown up on all the business cards John and Sherlock had seen. John turned the note over and found a few scribbled notes that almost looked like gibberish – 500p x 600p, #C0C0C0, 75º, 85mm x 55mm, 300g/m2, black, x50… He found himself typing everything into Google to find out what it meant, and when he did, he closed everything on the computer and ran upstairs to find Sherlock.

The detective was in the mystery section, glancing over every call number, author, and title on the shelf before moving on to the next one. "Hey," John started. Sherlock seemed not to notice. John stuck the post-it in front of his face. "I think she designed the cards here." That got Sherlock's attention. He grabbed the note from John and skimmed over the back and then the front, and then looked at the back again and held it up to the light and about an inch away from his face.

"Well, that's very useful." He folded the note and tucked it into his jacket.

"What is?"

Sherlock sighed. "She was anxious, in a hurry, and knew exactly what she was doing, at least when she wrote this. I spent a week brushing up on handwriting analysis two years back."

John nodded. "Does it tell us anything useful? When she was here, for example?"

Sherlock looked a bit put off to have what he'd said labeled irrelevant, but he looked at the paper again. "Somewhere between eight and ten weeks ago." He glanced up at the ceiling. "Might not hurt to ask for camera footage…" he muttered. "Come on, then."

They went down to the front desk, Sherlock played his "someone owes me a favor" card, and five minutes later, they were looking at footage from two and a half months ago. Sherlock opened different dates in four windows and clicked fast-forward a few times.

"I don't see how you're going to – " John started, only to be shushed by Sherlock. So John took a step back and picked up a book that was laying around while Sherlock looked for her in the footage.

"Got it," he said ten minutes later. By the time John had put the book down and stepped back over to the screen, Sherlock had closed three of the videos and enlarged the fourth. It was, without a doubt, the girl now known as Moriarty sitting at the same computer John had found the note at. Timestamps indicated that she was there for less than half an hour between one and one-thirty that afternoon. They watched her mess around on the computer, make a phone call, and then get up and leave. She only spoke to one person who walked into the room and sat down next to her for a minute. Sherlock called someone over to ask for an ID and learned that the person didn't work there. "Someone outside, then. She set up a meeting with him," Sherlock decided. He sent the file to his inbox to look at later. The video was paused, but he sat there and started off into space for a few minutes before standing up rather abruptly and rubbing his hands together. "Well, that was very informative," he said, and for a minute, John couldn't tell if he was being sarcastic or not. "Three o'clock," he said. "Coffee? We parked at a café."

"Sounds good," John agreed. John thanked the woman at the desk as they left the building. The sun was clear in the sky now, and it had warmed up quite a bit since the rain in London. The area seemed to have grown much busier in the half-hour they'd been there, so there was a bit of a line in the café. Sherlock ordered for them and they took a table by the window. "Now, were you seeing something invisible to the rest of the world on that tape, or was it really the waste of time it seemed to be to me?" John finally asked.

Sherlock shrugged. "The note confirmed a few things about her psyche. I'll get the name of the printing company she used when I can enhance the picture at home in case there's anything there. The only thing that really seems useful is the man she spoke to, though. I'll have Mycroft run it through some facial recognition software when we get home."

"Doesn't Scotland Yard have that sort of stuff?"

"Well, yes, but the legal ones aren't any good," Sherlock answered. The "obviously" didn't have to be said; it was still there.

They sat in silence for a minute before John asked, "Doesn't Mycroft worry about you getting involved with dangerous sociopathic homicidal criminal masterminds?"

"I think he knows by now that I'm past the point of no return with her. I'm seeing this one through to the end, and I think he also knows that that's going to result in one of us dying."

"Seriously? A fight to the death?"

Sherlock took a few sips of coffee before answering. "It's obvious, isn't it? She's clearly not going to be stopped by any sort of legal threat, I seriously doubt any jail could hold her longer than she wanted to be there, and she's the most arrogant person I've ever met. She won't stop until she's dead, and she's made it clear she's not going quietly. One of us will be dead before it's over." He read the worry in John's face, though. "Don't worry. I'll make sure it's not me."

"You can't promise that," John said quietly, thinking back to his days in Afghanistan.

"John Hamish Watson," Sherlock started. "I am personally promising you that Moriarty is not going to kill me. Not now, not ever."

"Just be careful with her, Sherlock."

"I will be."

They finished their drinks in silence. Sherlock stood up first and John followed him out to the car. Sherlock's lockpicking was getting better every time he did it – twenty-four seconds to get back into the car. He hotwired the car, started a playlist of his favorite violin music, and started the long drive back home.