Disclaimer: I'm pretty sure we should all defer to Conan Doyle, but I'll defer to Moffat too, just in case.

The case was a strange one, to say the least. The serial killer's victims were children between the ages of six and eleven, always found dead on playgrounds after having been strangled or poisoned. That made it sound like it was the sort of case that mothers always referenced to their children when telling them not to talk to strangers, but the case was more bizarre than the standard cautionary tale. All of the children who had been found dead so far had been bound to swing sets, tied to the chains at the wrists, shoulders, and waists to keep them from slipping from the position in which they had presumably died.

Sherlock was having more trouble with this case than he typically had. Usually, cases involved adults, and motives for lower-level operatives (everyone but Moriarty, really) were simple: jealousy, greed, secrecy, necrophilia, carrying through on a threat, etc. As much as Sherlock didn't understand adults, he could navigate them passably; children, on the other hand, were too confusing to even begin to ponder. Though the killer in this case was likely an adult, its involvement of children exceeded Sherlock's comfort threshold.

That was why Sherlock had asked John to accompany him to a playground.

"What does one do at such a place, exactly?" Sherlock asked as the two of them walked to the playground nearest their flat, the autumn wind causing his coat to flap and billow behind him.

"You play."

"I don't understand."

"You go on the equipment. It's usually more fun with other children. You chase one another around and have contests and talk while you do so. When you're little, large changes in position and speed can be frightening, so playgrounds are a source of adrenaline before you can handle big thrills."

"Why do you chase one another?"

"Why do you and Mycroft try to show each other up?"

"Oh."

"Right."

They arrived at the playground. It was deserted, probably owing to the fact that the breeze in the past few days had turned into a stiff, cold wind from the north that boded of winter. A set of four swings rose from a bed of wood chips near the sidewalk, while slides, a jungle gym, and monkey bars lay farther in from the street. All of the equipment appeared to be made of metal, with the exception of the parts that had to be rubber or plastic, and most of it was covered in peeling paint in primary colors. The whole place had a somewhat run-down and abandoned look, but the slides rubbed shiny by the passage of many small bottoms and the monkey bars free of paint in the middle lent a well-loved milieu to the place as well, as though the playground were a cast-off old teddy bear that had once been a favorite.

"I've never been on swings before," Sherlock said as he sat down on one.

"No time like the present," John replied, taking the swing next to Sherlock.

"What does one do on swings?"

"You pump your legs." Sherlock looked confused, so John continued. "Like this. It builds up momentum while you're traveling forward and backward. The point is to get as high as you can."

Sherlock tried, and John racked his brain to come up with any other circumstance in which a man in a suit would be playing on a swing set. For a few minutes, the two merely swung together, not talking. John, for one, wanted a few moments' pause from thinking about the case. Perhaps, just once, an idyllic moment wouldn't need to be ruined by macabre thoughts.

"We're married!" John exclaimed after a while.

Sherlock jumped off the swing, his lean, lithe body arching for an airborne moment before crumpling gracefully as he landed, picking himself up before John even had time to wonder if he was hurt. "What?"

"It's . . . it's what kids say. You know, when their swings line up perfectly and they're going back and forth together."

"I see. So you are not indicating that you believe us to be legally bound to one another until death or divorce do us part?"

John dragged his feet, slowing the swing and reducing its arc. "No."

"Pity."

John stumbled off of the swing. It was his turn to ask, "What?"

For perhaps the first time that John had seen, Sherlock blushed. "Nothing."

"No, really, what?"

"It's a pity. That we're not married, I mean."

John took a deep breath. "We're not even involved."

Sherlock began to pace with such ferocity that he kicked up sprays of wood chips behind him with every step. "'We're not involved'? Of course we're involved! You're involved in everything I do, and vice versa. You come on cases with me; you help me solve them. You write about me for the public. You cook for me; we eat together. You know my secrets, my associates, my enemies, my family, my quirks, and my obsessions. And you share them with me. My associates and enemies are yours, and your interests are mine. We share a flat, food, money—even a job! How much more involved can you get?"

"I meant . . . we're not involved . . . romantically."

"And when was your last successful relationship?"

John had no answer.

"And I consider my only relationship, ever, to be what I have with you."

"We're not . . ."

"Would you be?"

"You're not . . ."

"The sort?" Sherlock tilted his head.

John sighed. "Right."

"And what if I were?"

John tugged at the bottom of his jacket. "Can you tell me what this is all about? I mean, really explain it, as if I were the slowest idiot you've ever met?"

"I, Sherlock Holmes, am in love with you, John Watson. I have been for nearly two years now; practically from the day I met you. You are the most important person in my life, and you matter to me more than I thought I would ever let any human matter. I appreciate you in ways that I never expected that humans could be appreciated. You make me feel differently than I ever have in my life. I do not even have words for all of the sensations you have given me. You are smarter than any other ordinary person I ever met, and you're a better person, too. I love sharing my life with you, and I'm glad of all that we already have. But I wish we had even more. I wish you'd stop dating that perpetual stock of insipid women. I wish we had more physical contact. I wish I could tell you how I feel without cringing at the thought of your response. I wish I could hear you say to me the things I think about you." Sherlock rocked back on his heels and eyed John.

John pursed his lips. "I . . ." He stared at his feet.

Sherlock spun on his heel and left the park, striding rapidly in the direction of the flat, coat flying behind him.

"Sherlock, wait!" John stumbled over his own feet, trying to get a footing in this ridiculous pile of woodchips. "Please!"

Sherlock stopped, his coat and scarf flapping.

"I love you too," John panted, catching up to his friend. "I just never would have . . . I mean, Sherlock . . . You never seemed . . ."

Sherlock gathered John up in a hug and nestled his face into John's shoulder. "Thank you. Thank you. Thank you."

Finally, the embrace ended, and Sherlock said, "I need to perform an experiment at the swing set. I want to see if it is possible that any of the children were strangled while swinging. Would you consent to be my test subject?"

John laughed. "And you wondered why I didn't think you were the sort."

A/N: Reviews and favorites would be exceedingly lovely. I'd especially cherish some reactions to the way I portrayed Sherlock and John's relationship here.