John stood in the middle of the living room at 221b, chewing on the side of his thumb in a nervous habit that infuriated Mary. The skin by the side of his nail was red and raw where he had peeled the layers of skin back with his teeth. It was a sign of stress, he knew, but it was less destructive than smoking, or drugs. Which brought him back to his reason for being back in the flat.

His second search of the day had so far been frustratingly unsuccessful . There was nothing in Sherlock's bedroom drawers, nothing hidden beneath the sugar in the canister in the kitchen, not even anything in the space beneath the loose floorboard in John's bedroom, where John had hidden his unlicensed Browning pistol at times. That sort of hiding place was of course far too obvious for a genius to lower himself to use. If John was going to find whatever was hidden in this flat, he needed to start thinking like Sherlock Holmes. His eyes travelled round the room, considering.

'The best place to hide something is in plain sight,' came Sherlock's voice in his memory. Bookcase? Now that really was too obvious, surely. His eyes trailed to the fireplace, and the Persian slipper hanging on the wall next to it. Sherlock's favourite hiding place for cigarettes. He wouldn't, surely? He picked it up and shook it out. Nothing. He pushed his fingers in as far as they would go, but the slipper was empty. He threw it to one side in frustration, then picked it back up and looked at it more closely. The slipper was relatively large, too large for his fingers to be capable of reaching the end. And yet they had. He pulled out his phone, and used the torch mode to illuminate the inside of the shoe. There was a material covered layer occluding the shoe five or six centimetres from the end, forming a potential space between this and the end of the toe.

Using a knife from the cutlery drawer, John prized the hidden layer free, and from underneath it pulled out a small white bag of white powder. He groaned. Stupid bastard. He hadn't wanted to be right, but here it was. The proof that he needed that this wasn't just a case after all. Sherlock had a habit, an itch that needed to be scratched, a reason to keep drugs in the flat.

He shook the bag as he took it into the kitchen. What was it, he wondered - heroin? Cocaine? Something else entirely?

He placed the bag on the wooden chopping board, and pulling a knife from the knife block, sliced into the bag. Then, reminding himself that he was no longer subject to the army's random drugs test, he dipped his little finger into the powder and touched it to his tongue. Cocaine was a local anaesthetic. It should make his tongue go numb. Heroin? He had no bloody idea what effect heroin would have in tiny doses. This substance tasted oddly sweet, but it also made his tongue go numb. Hang on - no, it fizzed. It fizzed and was sweet. It reminded him oddly of - he dipped his finger in again, a larger amount of white powder this time and touched it to his tongue, then stared at the powder in disbelief.

Sherbet.

The stupid bastard had put sherbet from a sherbet fountain in a plastic bag and hidden it in the toe of the slipper. A false trail. But why? Just to piss off Anderson or more likely Mycroft if they came looking?

But John knew Sherlock. Knew about his love of the double bluff. If he had taken the trouble to hide fake drugs, then there had to be real ones somewhere. There had to be. The false ones would be an elegant decoy away from the truth.

More determined now than ever, he rifled through the kitchen cupboards. He knew what he was looking for now. Hidden compartments, secret backs to drawers, anywhere that Sherlock could have kept a secret stash. He drew a blank. The bedrooms and the bathroom were the same, nothing even on a second sweep. Back to the living room and even the bison's head proved devoid of secrets.

'Dust, dust is eloquent,' he heard Sherlock's voice saying. His eyes skimmed the bookshelf, looking for gaps in the dust line, evidence that any of them had been moved recently, but the only gap that he could find was in front of the book on drug addiction, that he had taken down himself only that morning. He pulled it off the shelf again, surely not even Sherlock would hide drugs in a book about addiction? He knew the answer to that. But a flick through the book proved it to be exactly what it seemed.

He looked again, so many books. He grabbed a chair and climbed up to reach the top shelf. He could find no break in that dust line, no clues there. Trying to think like Sherlock, he plucked several books off the shelves and leafed through them. 'Criminal Law' proved empty, so did 'Speed, Ecstasy and Ritalin: The Science of Amphetamines', 'Learning to Fly in 21 days' and all three volumes of Hansard.

And then he saw it, tucked right into the upper right hand corner of the book shelf, with a thick layer of dust on top of it - false dust? Would Sherlock go that far? 'The Pickwick Papers', a old copy, leather bound. But Sherlock hated Dickens, he had told John that many times. So why keep the book? John pulled it off the shelf, having to reach almost to the point of over balancing to grab it, dislodging a thick layer of dust with it, that made him cough.

He leafed through from the front, then the back. Several of the pages in the middle seemed to be stuck together, or were they? A quick exploration with a kitchen knife revealed something solid in the middle of the book. John ran his finger down the spine of the book and was rewarded with a click, as the lid of the secret compartment sprang open, and revealed - two small white bags of powder and a 'One Hit' kit*, still intact and sealed in its sterile bag .

John felt sick. He sat down on the chair hard, staring at the contents of the compartment. Then he cut into one of the bags and touched the powder to his tongue for the second time that day. This time there was no sweet taste, no fizzing, just numbness. Fuck.

Snapping the lid shut again, he bundled the book into his bag, doubled back at the door to pick up the bag of supposed sherbet just in case, and headed for the lab and Molly.

*'One Hit' kits (other brands also exist) are fairly widely available at needle exchange programmes. They contain a sterile metal spoon, an alcohol wipe, small sachet of citric acid, a syringe and needle, and sometimes a filter. Everything that is needed to 'cook up' heroin safely in fact, as the biggest risk comes from introducing infection with dirty kit. I hope I don't need to add that I am not for a second advocating the use of illegal substances with this chapter.

Thanks, as ever, to Sevenpercent. What would I do without you? Although I still couldn't resist using the Persian slipper, obvious as it might be, which is where Holmes stores his tobacco in the original canon, much to Watson's disgust.

The books on the shelf in 221b are all really there in the BBC series - someone much more diligent than me has produced a full list, which you can find on Tumblr under the 221b books tag. The exception is Pickwick Papers which isn't there (although Jane Eyre bizarrely is). I've borrowed that from Madness and Memory. The idea of Sherlock using the same book for his stash in both stories proved irresistible.

As ever, thank you for reading. It was everyone's encouraging comments, both here and on A03 that have brought me back to this story.