The thing that got his attention was that there was nothing to get his attention.

Sherlock gave a full body twitch as he became conscious. No sound had woken him, no odor or flicker of light had seeped into his psyche to alert him to his situation.

He had heard people talking about their "worst fears" before. When they were younger, Mycroft had been terrified of spiders. Sherlock had taken advantage of this fear and collected little arachnids everywhere he went so he could place them in Mycroft's clean laundry, or under his bookcase. That had been a valuable lesson for Sherlock in exposure therapy. When Mycroft was fifteen, he had walked straight up to Sherlock holding a little brown Tegenaria duellica in his hand. The next day, Mycroft had awoken with a start to find a garden snake in his bed.

It seemed that most people had a great fear, sometimes even a phobia. Lestrade was afraid of stepping on sewer grates. Anderson couldn't stand lizards. John didn't like small spaces.

But this-being devoid of sensory input with nothing to divert his mind from its constant churning-was Sherlock's worst fear.

He tried to take deep, slow, relaxed breaths, as he felt himself huffing short gasps through his nose. Categorize the stimuli, he told himself. Find a way out.

He was blindfolded, pointlessly since beyond the cloth there was still more darkness. It was definitely an isolation tank, then. It was like being suspended in watery gelatin. The water wasn't cold; pity, it would have been a welcome distraction. His ears were plugged up by some type of foam or spongy material. Sherlock kicked his foot out to make an experimental splashing noise and was more than a little disturbed that he couldn't hear anything but a low rumble from the tank's motor.

His arms were fastened into metal bracelets attached to a belt around his waist. He made a trial pull at the restraints on his wrists, but the belt didn't give any slack. Other than the belt, he was naked, only warm, sluggish water surrounding his form.

By far the most intrusive part of the confinement was the strip of cloth tied around his mouth. Sherlock could taste the saltiness of the water that had seeped into the gag, expanding it to fill his mouth. He pressed at the cloth with his tongue, concerned that a corner of the fabric was tickling at the back of his throat. The cloth shifted slightly, but couldn't be removed entirely.

Sherlock could feel his foot jerking in agitation. This was overwhelming at the same time as it was not enough of a stimulus. He squeezed his fists and released them repeatedly. A slight wave of nausea was a welcome distraction. But, it was fleeting and soon he was left in Purgatory, an abyss of existence.

He realized that he had no idea how he'd gotten into the tank, or who had stripped and bound him. He searched the last spotted memories he had but nothing was discernible.

Sherlock decided to attempt to push the lid of the tank open. He raised his feet into the space between the water and the wall of the tank and touched the smooth surface. He pushed, but nothing happened. He pushed harder but only managed to dunk the top half of his body underneath the water. He almost couldn't right himself and when he did, sputtering and shaking, he decided not to try pushing on the lid anymore.

Sometimes he was drifting. Sometimes he was in a lofty awareness. Sometimes he was unsure what he was doing. His skin itched. No, his skin positively crawled. He couldn't even hear himself breathing and the only smell in the tank was the vaguely acidic odor of the Epsom salts.

Time passed in enigmatic increments. And Sherlock's mind had nothing to distract him from the looming shadows that he didn't want to face. He tried focusing on the person or persons responsible for his current treatment. Moriarty? Hasn't piped up in months. Garden variety criminal of London? Too idiotic to pull off something this…devious. Mycroft? Hopefully knew better than to do this to his own brother, knowing what a terrifying ordeal it would be. There was no direction to take the problem. He hadn't any avenues to entertain.

Sherlock sucked in a shuddery breath through his nose and shoved the thoughts away. But they only came back at him more intensely. Freak. Psychopath. Not clever enough. Not good enough. You've let me down again, Sherlock. Outcast. Loner. Monster. Heartless. You're a failure. You'll never make anything of your life. You're insignificant.

He tried to sleep. The churning thoughts kept hammering away with him, depriving him of an escape.

Finally, something managed to distract him. He thought he saw a flash of light go off somewhere in his peripheral vision. He opened his eyes and stared through the blindfold, struggling to see, trying to figure out if the tank had been opened. Then he saw a face flickering before him, stark white against the blackness that filled his vision. He might have groaned, too difficult to tell. He shuddered and closed his eyes back, trying to make the image go away. It's a hallucination. You expected this. It's fine.

It wasn't fine. Colors and faces streamed across his brain, forcing themselves into his visual mind. Sounds were suddenly breaking through the barrier of the plugs. Horrible screeching sounds and low murmurs and gruesome screams. Sherlock stilled himself, even as he could feel his body trembling in the water. He tried to shut it out. He wished for his churning thoughts again. Anything was better than suffering from the hallucinations.

Then without warning, the faces were familiar. April, the dead six year old he'd been too late to find. The taxi driver, with his throaty laugh and sinister eyes. Mycroft, his expression unreadable, confronting him about his drug use. John, looking disappointed when Sherlock was unable, yet again, to connect to him or anyone else emotionally. All he could hear was the deafening sound of explosions and gunfire. His skin was being pricked all over with needles, his eyes were burning and his throat was closing.

Something grabbed him by the arm and he fought against it, even though he was aware that it wasn't real. The grip loosened and Sherlock plunged backwards under the water, sucking salty liquid in through his nose. He sputtered when he resurfaced, shaking his head to drive the water out of his sinuses.

Then, if he could be pardoned for the colloquialism, there was light. Shapes and objects were visible again. He could see tendrils of his hands that had swept over his face. He could see the ceiling some 50 metres above. The lid of the isolation tank was pushed back, quelling the claustrophobia and nightmarish visions.

The gag was removed from his mouth and Sherlock took the first decent breath he had in what felt like a very long time. Now two sets of arms were pulling him straight up and out of the unbearable tank. The restraints and belt were removed. He was settled onto the floor on a towel and given a cotton robe to wrap around himself. It was a few minutes before he realized that John was sitting right in front of him and talking. Wide-eyed and alarmed.

It took a few more moments before he figured out why he couldn't hear what John was saying. He pinched the ends of the ear plugs and pulled them out, dropping them carefully onto the towel.

" 'lo…" he said by way of greeting.

John sighed. "Thank God you're all right. We were beginning to think you'd been in there too long." He was rubbing the sleeves of the robe against Sherlock's arm.

"I'm not cold," Sherlock said. "And I was in there too long."

"Eighteen hours," John confirmed.

Sherlock's eyes widened slightly and then he regained himself. "Is that all?"

"You've got Mycroft to thank," John added. "We never would have found you otherwise."

"Where…are we?" Sherlock asked, looking around for the first time. It looked like a spa.

"Sweden," John answered. When Sherlock raised his eyebrows, he said, "Yeah."

"Well, it's about time we went back to London," Sherlock said flatly, attempting to hop to his feet. John steadied him. Then Sherlock noticed Lestrade and several generic police officers standing around and staring. "How long was I missing?" he asked.

"Four days," John said, his breath shaky. "It was a nightmare."

Sherlock scoffed at that but didn't say anything. Then, to John's great surprise, he ducked and let out a little yelp. John put an arm around his shoulders and supported him. "What is it?"

Sherlock swallowed a thickness in his throat. He shook his head. "Holy God…" he mused. "I'm still hallucinating."

"Temporary," John assured him. "Take it easy."

"All the respect I have for your profession notwithstanding, John, I do not intend to 'take it easy' ever again."