Two days later

"Sherlock? What…exactly are you doing?"

"What does it look like I'm doing?"

John took inventory of the things sitting on the table. "It looks like you're dissecting my umbrella. My poisonous umbrella. That's one thing I never thought I'd say."

Sherlock didn't look amused. "That is, in a sense, exactly what I'm doing. Why is it that you people never believe your own eyes?"

John was used to this kind of remark and certainly didn't take it personally. In fact, he was glad things were back to normal.

"So?" John asked. "What're you finding?"

"Ingenuity."

"What?"

"I'm finding ingenuity. Whoever designed this was clever."

"Isn't it just an umbrella?"

Sherlock shook his head. "No. It was crafted to look almost exactly like yours, but it isn't."

"So? How does it work? I did nearly get killed by it, I'd rather like to know."

Sherlock pulled his gloves off. "Pseudaconitine," he began, "is very slightly soluble in water. It's even more so in alcohol. Your umbrella—or what looked like your umbrella—contained both alcohol and the poison. The inside had been made into a carrying compartment specifically for these two things. Near the top was just a few millilitres of alcohol. It was suspended in a thin, collapsible tube that ran down the length of the umbrella. The poison was kept, in solid form, in the handle. The top of the umbrella had a small hole which allowed rainwater to run into the stick, collect the alcohol—water and alcohol are miscible, of course—and flow to the handle. The handle was very slightly porous, which allowed the mixture of poison, alcohol, and water to move outward to the carrier's hand. So slight they would barely notice, but enough to give a gradually lethal dose."

John raised his eyebrows. He took in this information for a moment and said, "Who did it, then? Do we know that?"

"I do not," said Sherlock, "so we definitely do not. I have a question for you, John."

"Hm?"

"Why atropine? Why did you have atropine in your beside cabinet?"

"Oh. Weird thing I'm still carrying around after the war, actually. I'm glad it's gone, to be honest—it was never useful. Until two days ago, anyway." He looked at Sherlock. "If you thought I was using it, you're mad. Or more so than usual. I hear it's quite nasty on its own. I certainly never expected it to save my life now that I'm here."

"Come now John, you really think I wouldn't have noticed if you started using a potentially hallucinogenic drug generally used to treat bradycardia? I know you a bit better than that."

"Sometimes, Sherlock," John said, "when I'm around you, I wish I could do drugs." He glanced down at the table. "For example, you do have splinters of wood, various test tubes, and no doubt small amounts of a very powerful poison all over the kitchen table, among the chemicals you normally have here."

For a moment, nothing was said. Then they looked at each other and both burst out chuckling.

"Boys," Mrs Hudson called from the stairwell, "the doorbell just rang. Can't you hear it? You might want to find out who it is."

Sherlock tossed his gloves onto the table and headed down the stairs. John followed.

When Sherlock opened the door, there was nothing there. There wasn't even anyone within fifty metres of the door. Sherlock stepped out, glanced around, and must have caught sight of something on the door.

John watched his friend pull a paper out from under the knocker and read it. "What's that?"

"That," said Sherlock, almost triumphantly, "is our murderer."

John frowned and took the proffered paper from Sherlock's hand.

It's been terribly fun to play with you, it said. I look forward to next time. -M