There were few things in the life of Sherlock Holmes that were more vexing than his association with River Song. From day one, she had been a mystery to him and her visits usually left him with more questions than answers. So when she arrived at his flat unannounced and requested that he play her a song, he begrudgingly agreed because the ends justified the means. And he was determined to solve her by any means necessary.

Sherlock lifted his violin, allowing his fingers and bow to dance across the strings in perfect synchronicity. As Time Goes By wasn't one of his favourites but he knew it well enough to play the song without any sheet music.

Once the song had ended, Sherlock opened his eyes and lowered his violin. When he looked towards River for a reaction, she was staring back at him with a forlorn expression and tears in her eyes. Feeling unnerved by her maudlin display, Sherlock set his violin to the side and his sights on his clue wall. River, perhaps feeling slighted by his sudden disinterest, unceremoniously departed shortly thereafter as quickly as she had appeared.

Contrary to popular belief, Sherlock wasn't completely apathetic. While it was true that he had mastered the art of indifference, he was more than capable of feeling things quite deeply. He simply preferred not to and therein laid the problem.

To borrow from the robot analogy so often and erroneously applied to him, Sherlock's brain was like a computer. It was organized, it was precise, and it operated in accordance with a stringent set of rules and standards. Emotions were like a virus. They infected and distorted the system. They corrupted, if not outright hindered, his ability to function. And that, of course, was where the drugs came into play.

He never used drugs for any pedestrian reasons such as chasing the euphoria associated with achieving a high. It was the numbness that Sherlock craved. The morphine and heroin granted him freedom from his emotions. And although he often felt the pull, he refused to indulge the whim at present. His drug use tended to only exacerbate the mawkish tendencies of the few he chose to hold close. Furthermore, he suddenly found himself gifted with a greatly welcomed distraction that arrived to the unwelcomed sound of unearthly wheezing.

Sherlock suspected that he would have recognised the TARDIS even if he had not heard about it from River. Granted, he may not have known exactly what the poorly disguised time machine was initially. He would have, however, been able to deduce that the telephone box that suddenly took up residence in his flat was not of ordinary origin nor had it arrived via ordinary means.

Sherlock walked a slow circle around the blue box. Its exterior, while seemingly unremarkable, stood as a monument to its history. The chips and nocks in the wood suggested untold tales of recklessness. River and her husband were obviously two of a kind.

Coming to a stop in front of the police box, Sherlock placed a flat palm against its wooden door. River had mentioned the Doctor's many faces. He wondered which one it would be today.

Not waiting for a formal invitation, Sherlock grasped the handle and pushed the door open. As promised, the TARDIS really was bigger on the inside. Impossibly so. The very idea of travelling through time was at odds with most of the logic that Sherlock held so dearly and the interior of the box was affront to the laws of physics.

In the middle of the visual chaos, there stood a man. He was tall with curly grey hair and brushy eyebrows, but he didn't resemble anyone River had ever described. "Which one are you?" Sherlock asked straight off, forgoing any pleasantries. "The oldest or the newest?"

"Well..." The Doctor began in an unexpectedly Scottish brogue. "Both, if we're being completely technical about it. I'm the most recent incarnation of myself and therefore the oldest."

"Semantics."

"The devil is in the details, they say," The Doctor told him with a smile. "But I suppose you would know that better than most."

"It's come up once or twice," Sherlock retorted as he scanned his surroundings. "If it's River you're after, you just missed her."

"Actually, Mr. Holmes, it's you that I've come to see." His voice was suddenly more serious. "It's about River..."

Sherlock lifted a brow, turning his attention back to the other man. His expression was not unlike the one River had worn before. The only difference was that his was more resolved than hers. Whatever had transpired wasn't as raw for the Doctor as it had been for River. They both were time travellers moving in opposite directions from one another. He must have come from a later point in time than she had. "She sent you?"

"No. Not River," the Doctor answered. He tapped a carved block of wood no bigger than a shoebox.

Sherlock strode forward out of curiosity. Upon closer inspection, he discovered that the wooden block was actually a box. "May I?" The Doctor gestured with an open palm. Sherlock lifted the box to his eye level in order to examine it further. There wasn't anything especially significant about it. He lowered the box enough to look the Doctor in the eyes. "Where did you get this?"

"River delivered it to my former self with instructions to bring it to you," he explained to Sherlock. "I would have come sooner but…situations quite frequently arise and alter my plans."

"I just saw River. Why didn't she give it to me?"

"I got the impression that she wasn't sure of that herself," the Doctor confessed.

Sherlock set the box back down on the console and slowly opened the lid. Inside, he found a blue diary like the one River always carried only this one was older and more tattered than he'd ever seen hers. Along with the diary there was also another object. It was small and long and the likes of which Sherlock had never seen before.

"Oh, River…" The Doctor exhaled in a breathy laugh to his side. "You clever girl!" He began moving frantically around the console pressing buttons and flipping switches. The ground beneath them shifted and the TARDIS began to make the same irritating noise as it had done when it first arrived.

"Where are we going?"

"I'd have thought you would have sorted that out by now," the Doctor said. "We're going to see River." He picked up the unnamed object. "And here's our invitation."

Once again, Sherlock found himself wondering what the urgency was behind him seeking out River when they had only just parted ways, but he resisted questioning the Doctor. Talking to him was a bigger headache than chatting with River. At least she wore her ambiguity better.

When the TARDIS began groaning again, Sherlock deduced that they had arrived at their destination. Deciding not to wait for the Doctor, Sherlock grabbed the box and diary and strode outside. He wasn't sure what he was expecting to find but endless bookshelves was low on the list. "You've brought us to a library?"

"Technically…you've brought us here," the Doctor countered. "And it isn't just any library. It's the Library."

"Explain."

The Doctor gestured to their surroundings. "Welcome to the Library, a planet-sized library built during the 50th century. Here you'll find a copy of every book ever written. Several of which are written about you," he added. "It's also the final resting place of Professor River Song."

The Doctor's words drew Sherlock up short. "Come again?"

The Doctor sighed softly. "You wanted to know why she couldn't deliver the message herself? There's your answer." He paused and gave Sherlock a look of condolence. "I'm sorry. I'm so sorry."

Sherlock waved off his words as nonsense. "River can't be dead. I saw her. I just saw her."

"Who you saw was a version of her," the Doctor explained. "People think of time as something that happens linearly and for the most part it does. But for people like River and myself, the progression is a bit more…complicated."

Sherlock allowed the Doctor's words to sink in. He closed his eyes and retreated into his mind palace to sort through the information he gleaned.

River, or a version of her, had sent Sherlock a message. One clearly from a point in time occurring further in the future than the River he had just seen existed in. A message River couldn't deliver herself and instead she trusted it to the Doctor. He opened his eyes and turned towards the Doctor. "You called that thing an invitation," he said pointing to the object still in the other man's possession. "Why? What is it?"

"This?" He held it up. "It's a sonic screwdriver. My sonic screwdriver. I gave it to River right before she came here to the Library." He glanced down at the screwdriver. "When I first met River…from my perspective…it was here. The day she died. She told me something only I could have told her and she had this." He held it up. "I knew I had to give it to her in the future because my past self already had seen it."

The look on his face told Sherlock that the Doctor had known he was sending River off to her death when they parted ways. More importantly, it was a look that Sherlock recognised. It was a look that mirrored the expression that River wore when she requested that Sherlock play a song for her only moments ago. It was a look of grief and longing and sadness. In short…it was a look of mourning. The Doctor was in mourning for River. And River…

"Where did she get the box?" Sherlock demanded.

"Perhaps that's a question best answered by River herself," the Doctor suggested. He led the way back inside the TARDIS. "River may be dead, but she'll never be gone. Not truly."

Sherlock exhaled sharply. "Is this really the time for sentimental drivel?" His own emotions were proving to be rather burdensome at the moment. He didn't have the patience to deal with those of River's widow as well.

"I was speaking literally," the Doctor informed him. "When she died, River was saved as a data ghost and uploaded to the Library's data core. Data that can be accessed at will!" He began fiddling with the console again aiming the sonic screwdriver at different odds and ends. "Put your hands right here," he instructed. Sherlock looked at the Doctor dubiously but complied. He set the box aside and placed his hands on a portion of the console that seemed to suck him in on contact. "You've just initiated a psychic link with the TARDIS. Through her, you'll be able to access the Library's data core. Just say…'access River Song.'"

Sherlock hesitated for a brief moment before repeating the words. "Access River Song." There was a sudden surge in synaptic activity and Sherlock was seemingly transported to a park. For a brief moment, he was confused as to why he had been brought there, but then he heard it. The dulcet tones of his favourite melody.

"'It is with a heavy heart that I take up my pen to write these the last words in which I shall ever record the singular gifts by which my friend Sherlock Holmes was distinguished,'" River read aloud to a group of children. "'In an incoherent and, as I deeply feel, an entirely inadequate fashion, I have endeavoured to give some account of my strange experience in his company from the chance which first brought us together at the period of the "Study in Scarlet"…'"

"Pink," Sherlock chimed in automatically. "A Study in Pink."

River gasped and froze momentarily before slowly lowering her book to her lap. "Every good writer knows they have to alter the details a bit when writing about real people, my dear," she said breezily as she turned to face Sherlock with a smile.

"Authors, journalists, bloggers," Sherlock replied with a sharp exhale of air. "All they care about is painting a pretty picture."

"People do love imagery," River shot back. "It sells the story."

Sherlock stared at her for a moment. He was feeling…wistful. It was strange and inconvenient, but was there any other way to be where River was concerned? "Tell me a story, River."

River closed her book and sent the children off so that she and Sherlock could have a moment alone. "I didn't think I'd ever see you again," she confessed.

"You only just left me," Sherlock told her as he took a seat next to her on the park bench. "You asked me to play you a song, As Time Goes By."

"Oh…I remember that day well." The look of mourning returned.

"Because it was the day that I died," he deduced.

"Spoilers," she sang back.

Sherlock huffed. "I hate it when you do that."

River chuckled. "Believe me. It's much better to be on the giving end rather than the receiving. You'll learn that one day."

Sherlock fell silent for a short time and then he spoke again. "Why did you bring me here?"

"You think I brought you here?" she questioned in surprise.

"The box," Sherlock responded impatiently. "A carved wooden box that to you gave to the Doctor to give to me," he reminded her. "One that contained your diary and the sonic screwdriver the Doctor gave you."

"Oh…" She gasped again. "Oh, you sentimental old fool," she marvelled. "That was it all along it, wasn't it?"

"Please do try to be more transparent for once," Sherlock begged in exasperation.

River smiled sadly. "On the day you died, you gave me the box and told me to return it to you….to your younger self."

Sherlock shook his head again. "How? Where did the box even come from? And where did I get your diary and the sonic screwdriver?"

"Here at the Library," she explained. "Don't you see? You summoned me to grant your dying wish, which was to return the box to yourself so you could find my diary here in the Library. So you could find me."

Sherlock frowned. "Why would I do that?"

"To say goodbye. Properly."

Sherlock's jaw clinched and he forced his facial muscles to relax. Sentimental old fool indeed. His future self seemed unrecognisable in comparison to the man that he was now. Would something transpire in the years to come that caused such a drastic change in demeanour? He wasn't sure if he wanted to know.

"What's a proper goodbye?" he questioned sincerely. "The last time I attempted to say goodbye, I rang John for a chat and faked my death. Needless to say, I'm not very good at them."

"We say it like we believe we'll see each other again," River told him. "One way or another…" Her voice wavered. "I will see you again because no matter what…I'll always come back to you, my dearest William. This isn't goodbye. It's so long until the next time."

Sherlock felt that unnervingly wistful feeling once more. Only now it coloured by mourning as well. He refused to let it take hold of him though. So he forced the feelings down deep, stood up with a flourish and inclined his head in River's direction. "Until the next time, Melody."

"Until the next time," she echoed back.

Sherlock's consciousness re-joined his body inside the TARDIS and he disengaged himself from the console.

"One last stop before we go," the Doctor announced, already halfway out the door with the wooden box in hand. He led Sherlock to a balcony deep within the Library where River's diary and sonic screwdriver sat undisturbed. He swapped them for the ones in the box. "I trust you know what to do with these," he said, passing the objects to Sherlock but leaving the box behind. Sherlock reckoned he had to procure one of his own eventually.

Sherlock looked down at the diary. "I always wanted to solve her and now I have all the answers at my fingertips."

"Half the fun of knowing River is the parts that are left unknown," the Doctor quipped while walking back towards the TARDIS.

"Aren't you the least bit curious?" asked Sherlock.

"Always," he confessed. "Which is why I avoid the temptation."

"I've never been known for my impulse control."

"I'm sure you'll sort it out. You're Sherlock Holmes, the great detective." The Doctor returned Sherlock to 221B only a minute after they had originally departed. Then, he made a hasty exit leaving Sherlock alone to contemplate all the events of the last few hours.

Sherlock retreated into his mind palace for an unknown of time before being pulled out by the sound of another unannounced guest. "Sherlock," Ms. Hudson's voice called out to him. "Be a dear and have a look at this for me." She shoved a carved wooden box at him. "It's a jewellery box. Or at least it was. I got it off a friend of mine. I don't really need it, but I thought to myself, 'maybe Sherlock could use it to store some of the things he uses for his experiments,'" she reasoned. "It'd definitely be better than just leaving them lying about like you usually do."

"You're absolutely right," Sherlock agreed, all but snatching the box away from her.

Ms. Hudson looked stunned. "I am?"

"Yes," Sherlock assured her while directing her towards the door. "You should treat yourself to a nice cuppa for your brilliant intuition. And make one for me while you're at it."

"Not your maid, love," she retorted as she started down the stairs.

"I'll have biscuits with mine, if you would be so kind," he shouted after her. Once she was out of sight, Sherlock placed River's diary and the sonic screwdriver inside the box. No sooner than he had tucked it away was he interrupted once more. "River, back so soon?"

"Counting the days, are you?" she teased.

Just by looking at her, Sherlock could tell that this River was younger than the previous two he'd seen that day. She was more carefree than the others. Clearly she had yet to live through the tragedies of her predecessors. "Days? It barely felt like minutes."

River beamed from ear to ear. "Fancy an adventure?"

Sherlock offered her his arm. "Where to this time?"

"I'm thinking Victorian London," River thought out loud as she slipped an arm around his. "I'm in the mood for a story and I hear Doyle has a real way with words."

"Are we dressed for that?"

"Good point," River retorted. "Grab your coat. I suspect that it may very well come in handy." Sherlock reached for his Belstaff with his free hand. "Ready?" she asked with fingers poised above her vortex manipulator.

"Always."