A taxi drive and few minutes searching the signs above the aisles of books was all it took for you and the boys to find the section the book Sherlock had picked up was from. The date stamped on the book was the same as the day Lukis had died, and although it wasn't much to go off on, it was enough to draw the group to where they were now. 

    The three of you quickly went to work checking the books, pulling some off the shelves and then sticking them right back in their places. Anyone who'd come to the library with the actual intent of reading would have had no clue what you guys were doing. 

     John pulled one book out and gasped. "(Y/N)!" You went over to see what he had found. Painted against the metal behind the books was a streak of yellow paint.

     Your eyes widened and you started pulling out more books beside it. It was the same symbol from the bank! "Sherlock," you called, "You better come see this."

[\\=//]

     Back at the flat now, the three of you were looking at the mirror above 221B's fireplace. New pictures of the scene at the library were now hanging next to snaps of the other graffiti. 

     "So, the killer goes to the bank, leaves a threatening  cipher for Van Coon, Van Coon panics and runs back to his apartment, locks himself in," Sherlock muttered. 

     You and John, who were significantly shorter than Sherlock, were standing a bit farther on either side of him so that you didn't have to crane your neck to see the pictures. "Hours later, Van Coon dies," John said.

     "The killer finds Lukis at the library," you spoke. "Writes the cipher on the shelf, where he knows it'll be seen. Lukis goes home..."

     "And late that night, he dies too," John finished. "Why... did they die?" 

     "Only the cipher can tell us," you whispered. 

[==\\/\//==]

     Almost an hour later, you and the boys were making your way across Trafalgar Square. The mist from the marble fountain in the middle created a pleasing effect that reminded you of going to the beach, the cool, tiny water droplets from the waves gently hugging your skin.

     "The world's run on codes and ciphers, John," Sherlock was explaining. "From the million-pound security system at the bank to the pin machine you took exception to, cryptography inhabits our every waking moment." 

     John shot Sherlock an annoyed look. "Yes, okay, but?"

     "But," you said, "it's all computer generated. Electronic codes, electronic ciphering methods." The group made its way up the stairs of the National Gallery. "This is different, though. Modern code-breaking methods won't unravel it." 

     "Okay, so.... where are we headed?" John asked. You shrugged. "Sherlock?"

     "I need to ask some advice," Sherlock responded. You cringed, but then started laughing. "What? Say that again?"

     "You heard me perfectly clear; I'm not saying it again," said Sherlock, annoyed. 

     John smiled. "You need... advice?"

     "Yes. On painting. I need to talk with an expert."

     "Well, hold on," you said. "Why didn't you ask me anything? I do arts all the time." It was true, you liked to draw a lot. 

     Sherlock shrugged. "I doubted you'd know anything of graffiti types. Hardly seems your style, does it?"

     You tsked. "Okay, true, but you didn't know that I don't know that. You just didn't want to have to ask me for help, didn't you?"

     Sherlock gave you a dark look as you and John started laughing. 

     He led you and your friend to the back of the gallery. A young man in a hoodie was busily spray-painting a door.

     "Part of a new exhibition," he said as the three of you walked up. 

     "Interesting," Sherlock muttered with a roll of his eyes.

     The artist took a step back and admired his illegal work. "I call it.... Urban Bloodlust Frenzy." He chuckled.

      "Catchy!" John commented sarcastically.

     He went back to spraying on his artpiece. "Got two minutes before a community support officer comes running round that corner." He looked round to Holmes. "Can we do this while I'm working?"

     Sherlock took out his phone and held it up in from of the young man. It was a picture of the graffiti at the library. In one fluid motion, the offender threw the can of paint in his hand to you and snatched the phone out of Sherlock's hand, inspecting it. The can landed in your still-bandaged hand, sending a dull ache through your palm. You half-mindedly tossed it to John. "Know the author, Raz?" Sherlock asked.

      The young man- whose name must've been Raz- shook his head. "Recognize the paint, though. Looks like Michigan. Hardcore propellant... I'd say zinc."

     "What about the symbols?" you asked, eager to move this along. Less than two minutes? Had to hurry this along. "Do you recognize them?" 

     Raz squinted at the phone. "Not even sure it's a proper language..." he muttered.

     "Two men have been murdered. Deciphering this is the key to finding out who killed them," you said impatiently. Are you going to help us or not?"

     "Well, it's not much to go on, is it?" Raz asked, still looking at the screen. When you didn't say anything, he looked up carefully, only to find your cold stare. "I-I'll ask around," he stammered, blinking several times. 

     "Somebody must know something about it," John reasoned. Then you heard running footsteps.

     "Oi!" Someone shouted. It was a couple of community support officers, racing toward the group. With a yelp, Raz dropped the can he still had and took off, you right by his side. 

     "City suckers!" Raz whooped excitedly as he ran to the officers. "It's a poLITICAL STATEMENT!"

     (Sometimes I wonder if I can even. Like literally can i like even? like omigosh seriously guys I like totally can't even. like if you agree lol like rofl #so relateable)