Warning: This story contains spoilers for season 7 and season 8 of Supernatural.

A STRANGE CASE FOR A STRANGE DETECTIVE

They say the first weeping angel was one who wept for Lucifer when he fell. He pinned and cried so much for his fallen brother that the Lord forsake him, too, for an angel shall not love Lucifer; especially not before our Father and his mortal children.

- a piece of paper torn from an unknown book; found in the diary of John Winchester

At precisely ten o'clock in the morning, July 3rd, John Watson awoke to the sound of clapping. Steady, slow, booming claps. He groaned and tried to bury himself deeper into the armchair where he'd dozed off after breakfast. He was having such a marvellous dream about... About...

"Get. Up. John!" cried Sherlock, his flat mate, punctuating each word with a clap.

"What, Sherlock? What?" John glared at him, raising his head to watch him charge around the room.

"Lestrade called. There's a case!"

A measure of life returned to John at these words. Wonderful. Another case. John hid a smile by rubbing his face. It had been well over a month since Sherlock had agreed to take on work, 'Boring! Boring! I want something interesting!', and despite how perpetually single minded Sherlock became during a case, John was pleased to see him excited.

"Where?" he asked.

"Peel Street," replied Sherlock. "Get your coat on, I've already called for a taxi."

Huffing, groaning and deliberately moving at a snail's pace, John wiggled into his slippers and did as Sherlock bade. It was always a pleasure to be needed.

The minute their sleek black cab pulled up, Sherlock was already out the door. "Come along, Watson!" he cried. John ran down the stairs after him, knowing Sherlock wouldn't hesitate to leave him behind if he dawdled.

"So, what is it?" John asked once on they were in the back seat.

"A missing person."

John waited for more, knowing this wasn't the kind of thing Sherlock found 'interesting'. "Yes?" he prompted.

"Third report this month, but the first report was in Scotland, and the second report in Dorset."

"That's opposite ends of the country!" John cried. "What ties them together?"

"A crack in their wall."

"What?"

"Exactly." Sherlock steepled his fingers, staring dead ahead out the windscreen.

"How long have they been missing?" John asked, despite recognising the far-away look in his eyes.

"A month, roughly, do pay attention. And be quiet."

Rolling his eyes, John held his tongue and watched the streets of London filter by. For the next twenty minutes, Sherlock ignored him, his eyes darting to and fro as he thought.

They entered Kensington and pulled up outside an average, terraced house on Peel Street; narrow and deceivingly small looking. John knew that the considerable depth of a Kensington house made up for its squashed width.

Sherlock bounded out the car, leaving John to pay. He held his breath and chose not to comment – he's excited, he's not sulking, just pay and then jump out first next time.

On the pavement, John waited and watched as Sherlock strode up and down outside the iron gate of number 188. It was cornered off with police tape and abuzz with curious neighbours, police sentinels and forensic scientists coming and going out the main door. By now, the constables of Scotland Yard knew Sherlock well enough to let him go about his own way.

With an air of nonchalance, Sherlock lounged up and down the pavement, gazing at the ground, the sky, the opposite houses and the line of railings. He took in the details almost affectionately.

John observed that the front garden of number 188 was neat and minimalist; a patio with a set of white, metal chairs and a table. Purple shrubbery hung under the living room window and everything was still speckled with water from last night's rain. The house itself was painted lavender blue, the door framed in white. Perhaps the prettiest house on the street.

As he did so, Sergeant Donovan charged out the front door. She spotted John first, then her gaze honed in on Sherlock with a barely hidden look of disgust. She chewed on her inside cheek and stomped over to John, her bushy hair bouncing on her shoulders.

"Figures you'd be here," she said, voice laced with contempt. "I didn't think this one would be bloody enough for him." Donovan shot a glare at Sherlock, who carried on scrutinising the shrubbery as if oblivious to her loud remarks.

"Yes, well," said John. Try as he might, every encounter with Donovan only deepened his dislike for her. Good sergeant, yes, very good at her job. Not so 'up there' on her manners or people skills. John couldn't help smirking. Not so different from Sherlock, actually.

"What?" she said, eyes narrowing.

"Nothing. But three cases linked together despite occurring at opposite ends of the country... Doesn't that seem like Sherlock to you?"

Donovan hmphed and crossed her arms. He saw Sherlock pause by the railing and smile, before spinning on his heel and marching into the house.

"Ah, excuse me," said John, and followed Sherlock inside.

In the hallway they were met by a tall, flaxen-haired man, with a notebook in his hand. He nodded to Sherlock and wrung John's hand.

"Gregson," greeted Sherlock, turning his back on the detective to examine the front door. Before Gregson could get in a word, he asked, "Who forced open the door?"

"We did, it was locked," replied Gregson. "I'm glad you're here. I made sure everything was left untouched."

Sherlock spun around to face him again. "Except that!" he answered, pointing at the wooden floor. It was covered in splotchy, dusty boot prints. "If a herd of buffaloes had passed along there couldn't be a greater mess. No doubt, however, you drew your own conclusions before you permitted this?"

Gregson faltered and John pursed his lips, always uncomfortable to be in the same room as these two. Sherlock did like to wind Gregson up. John studied the floor instead, clasping his hands one over the other.

"I've had so much to do inside the house," Gregson cried. "Lestrade is here. He was supposed to look after this, not me."

Sherlock glanced at John and raised his eyebrows sardonically. "With two such men as yourselves on site, there won't be much for a third party to find out," he said. His tone could so easily be misconstrued as complimentary, and as expected, that's how Gregson took it.

Gregson rubbed his hands together in a self-satisfied way. "I think we've done all that can be done," he answered, "it's a weird case though, and I knew your taste for weird."

"It's a wonder you bothered to call at all," said Sherlock, dripping with so much false pleasantry even Gregson noticed. "Shall we?" With that, Sherlock pushed him aside and headed into the kitchen at the other end of the hall. John squeezed past as well, thought to apologise for Sherlock, but found the words caught in his throat. Never mind.

The kitchen was stylish and had polished countertops with a separate area for a tiny dining table. Whoever lived here kept the place in good order, or so John suspected. It was hard to tell with half a dozen forensicists crammed in, their tool kits spread out on all available surfaces.

"Lestrade!" cheered Sherlock, brushing past the greying Detective Inspector and heading straight to the fridge. It was always hard to tell with Sherlock, but John had a hunch that Lestrade was his favourite member of Scotland Yard.

"It's about time," said Lestrade, "we're almost done here."

"Is that why you let everyone traipse through the hallway?" asked Sherlock from the depths of the fridge.

"Well they've gotta traipse somewhere. Look, there's nothing here. The crack is upstairs, in the bedroom."

Sherlock shot up straight and shut the fridge. "The crack," he said slowly, analysing the calendar pinned onto the door. "What an eloquent name. I hope your wife named your children and not you."

John stifled a laugh. Sherlock was certainly in an excellent mood.

"Thanks very much," replied Lestrade.

With a tight smile, Sherlock cast a glance around the rest of the kitchen, eyes darting everywhere, before striding back into the hall. He crossed the space in three long strides and leapt up the stairs, taking them two at a time. John, Gregson and Lestrade hurried to keep up.

"Who lived here, then?" puffed John, casting a glance down at Lestrade close behind him.

"An Amelia Pond," he replied. "She's a model and was involved in a perfume campaign. Petri... Petri-something."

Gregson barrelled John and Lestrade aside, desperate to be the first one into the bedroom with Sherlock.

"Petrichor," Gregson puffed. "We'll never get anywhere if you don't remember the details, Lestrade." He broadened his chest with pride and disappeared through the third door on the landing.

Lestrade clenched the top of the banister. "Always a bloody contest with him," he muttered to John. "Go on, after you. Can't deprive Sherlock of the only one who actually understands him."

"I don't know about that," John replied, despite feeling his stomach swoop with joy. He tried not to measure his worth gauged upon the appraisal of his partnership with Sherlock, but sometimes he couldn't help it. Who wouldn't want to be known as the only man who truly understood Sherlock Holmes?

Ms Amelia Pond's bedroom, on first glance, looked cluttered. Nothing like the cleanliness they'd left behind in the kitchen. Blue walls and simple décor, but covered in memorabilia. A vanity-table stood in the corner, buried beneath hand-knit dolls of a man in a bow-tie; most propped up against a miniature, cardboard police box. Probably something from her childhood.

The shelves were stacked with books, many of them bright and colourful, like children's books, and the window was half blocked up with a stack of yellowing volumes. Clothes were slung over the end of her bed railing, across her vanity stool and on the floor beside her nightstand. Above her unmade double bed, hung a picture of a Roman tugging along a giant stone block. A woman of history, perhaps, and who lived a chaotic lifestyle.

And there, on the wall opposite the Roman, was a jagged crack running through the brickwork. John had to admit, it was an impressive size – nothing like the hairline fissure he had been expecting. What could be so significant about a crack in someone's wall? He still couldn't tell, and felt eager to hear Sherlock's thoughts.

Lestrade and Gregson hovered by the offending mark, staring at it as if confronted with Sudoku. Sherlock, however, continued to inspect the whole room first.

"There's a ring here," said Lestrade, staring between his feet. "I made sure it wasn't moved. It looks like a wedding ring."

At this, Sherlock stopped stroking the half-dead house plant on top of the chest of draws and swept over. He threw his navy trench coat out behind him and crouched down to the ring. John and the others stepped back, giving Sherlock space to twirl it between his fingers.

"She was recently divorced, I take it," said Sherlock. "There are no signs of a man living here. She still loves him, too, otherwise this would be hidden in a box, buried in a draw out of sight. She keeps it out to admire... The ring is shiny, so she probably plays with it a lot, keeps it in her pocket or on her nightstand.

"The question is, why is it here, on the floor, and not with her? She takes care of things with sentimental value." He rose to his feet and nodded at the knitted dolls. "Unlikely they're a gift, she doesn't keep pointless decoration, so they must mean something to her. The dolls, plus the numerous children's books around her room, makes me suspect she wants children, but her partner didn't, so they divorced."

"Yes, she was married to a Rory Williams," said Lestrade. "I don't know about the children part."

Gregson scoffed and bounced on the balls of his feet. "Doesn't seem like a wild conclusion to me."

"I didn't say it was," shot Lestrade, grinding his teeth. "But that still doesn't answer the real question. Where did she go, and how did this crack get here?" He jabbed his finger towards the wall, as if he wanted to shove Gregson through it.

Trying his best to block out the two detectives, John stood back to get a better look at the wall. His brow furrowed, and he turned in a complete circle, taking in the whole room again. Well, that was odd...

Sherlock smiled at him and caught his eye. "What are you thinking?"

"Her room's a complete mess, well, she doesn't seem organised, anyway. But that space there..." John waved his arms, trying to encompass the floor space beneath the crack. "It's empty. No boxes, no socks, no books. This whole section of the room is bare."

"Very good, John," said Sherlock, full of enthusiasm and none of it patronising. John kept his serious-business face in check, hiding the pride that bubbled up inside.

"For some reason," Sherlock went on, "Ms Pond avoided this area, probably subconsciously. This crack hasn't just appeared. It's been here since she moved in."

Gregson and Lestrade shared a look. John could already figure out that if a crack tied together three missing person reports from across the country; then that crack had to be identical in all three instances to draw attention; or be in the exact same sort of room; or represent something, like a graph. It could not have been here all along.

The three of them were all thinking the same question. Gregson was the first to voice it. He pulled out a photo from his shirt pocket and pressed it to the wall.

"How is that possible?" he cried. "This crack is exactly the same shape and diameter as the two found in Scotland and Dorset. I'm telling you, it's a signature. Someone is abducting these people and leaving these cracks behind as his or her mark."

"Right," said Lestrade, standing firmly beside Gregson on this one. "You'd need tools, time, probably a stencil to get the same shape. Two coincidences? Sure. Three? These cracks are deliberate and the fact that they're found in the homes of three missing persons makes it unlikely that these cracks are here by chance."

Sherlock only smiled at them; the one smile that infuriated everyone. It deepened his eyes and stretched his lips thin, it said: I know something you don't know. You're looking at it wrong. How adorable.

"He's right," said John, also not a fan of That Smile. "How can this crack be identical to the others if it's always been here?"

"I don't know," beamed Sherlock. "But that, my friend, is the right question." He went up to the wall and pressed his ear to the crack. They waited in silence. "What's on the other side?" he asked after a moment.

"Next door's bedroom," answered Lestrade. "Why?"

"I can hear...a whisper..." Sherlock beckoned John closer to listen as well, but he hesitated.

"Sherlock, you can't just eavesdrop on someone's bedroom!"

Sherlock cast him a drivelling look, one that made John shrink inside. Sighing, he pressing his cheek to the wall, too. They stared at each other as they listened. It was extremely rare that Sherlock's eyes were near level with John's, and for a moment he thought, huh, his eyes are a nice shape, before looking away to concentrate.

A thin, cold stream of air tickled John's face. It leaked from the crack at a steady flow, as if it were part of a cave entrance.

"It's just the wind," he said. "But yeah, it sounds a little bit like garbled voices. You could say that about seashells though."

"But where is the wind coming from?" asked Sherlock.

John pressed his mouth shut, unable to answer. Smiling again, Sherlock strode the door and paused to give Lestrade and Gregson stern looks. "I want someone to knock through that wall," he said. "See what's going on in there. Wires, probably. A miniature camera, or maybe a means of communication."

"We can't just—" began Lestrade.

"Let me know what you find!" And with that, Sherlock pocketed Ms Pond's ring and darted from the room.