The Blackthorn Key

“It’s in code,” I said.

He sighed. “Why is it always in code?”

“Because other apothecaries will do anything to steal your secrets. When I have my own shop,” I said proudly, “I’m putting everything in code. No one’s going to swipe my recipes.”

“No one will want your recipes. Except poisoners, I suppose.”

“I said I was sorry.”

“Maybe this is in code,” Tom said, “because Master Benedict doesn’t want anyone to read it. And by ‘anyone,’ I mean you.”

“He teaches me new ciphers every week.”

“Did he teach you this one?”

“I’m sure he’d planned to.”

“Christopher.”

“But I figured it out. Look.” I pointed at the notation ↓M08→. “It’s a substitution cipher. Every two numbers stand for one letter. This tells you how to swap them. Start with ‘08,’ and replace it with M. Then count forward. So 08 is M, 09 is N, and so on. Like this.”

I showed him the table I’d worked out.

A

20

B

21

C

22

D

23

E

01

F

02

G

03

H

04



I

05

K

06

L

07

M

08

N

09

O

10

P

11

Q

12



R

13

S

14

T

15

V

16

X

17

Y

18

Z

19



Tom looked between the cipher and the block of numbers at the top of the page. “So if you replace the numbers with the right letters . . .”

“. . . You get your message.” I flipped the parchment over to show the translation I’d inked on the back.

Gunpowder

One part charcoal. One part sulfur. Five parts saltpeter.

Grind separately. Mix.

Which is what we did. We set up on the larger display table, farther from the fireplace, based on Tom’s reasonable suggestion that gunpowder and flames weren’t friends. Tom moved the bleeding spoons from the table and got the mortars and pestles from the window near the bear while I pulled the ingredient jars from the shelves.

I ground the charcoal. Sooty clouds puffed into the air, mixing with the earthy scent of the dried roots and herbs hanging from the rafters. Tom, glancing uneasily at the front door for any sign of my master, took care of the saltpeter, crushing the crystals that looked just like ordinary table salt. The sulfur was already a fine yellow powder, so while Tom swirled the ingredients together, I got a length of brass pipe sealed at one end from the workshop in the back. I used a nail to widen a hole near the sealed end. Into that, I slipped a loop of woven, ash-colored cord.

Tom raised his eyebrows. “Master Benedict keeps cannon fuse?”

“We use it to light things from far away,” I said.

“You know,” Tom said, “things you have to light from far away probably shouldn’t be lit at all.”

The mixture we ended up with looked harmless, just a fine black powder. Tom poured it into the open end while I propped up the pipe. A narrow stream spilled over the side, scattering charcoal grains onto the floor. I stamped the powder in the tube down with cotton wadding.

“What are we going to use for a cannonball?” Tom said.

Master Benedict didn’t keep anything in the store that would fit snugly in the pipe. The best I could come up with was a handful of lead shot we used for shavings to put in our remedies. They scraped down the brass and landed with a hollow thump on the cotton at the bottom.

Now we needed a target, and soon. It had taken a lot longer to put everything together than I thought it would, and though I’d assured Tom that my master wouldn’t return, his comings and goings weren’t exactly predictable.

“We’re not firing this thing outside,” Tom said.

He was right about that. The neighbors would not look kindly on lead shot flying through their parlors. And as tempting a target as the stuffed beaver on the mantel was, Master Benedict was even less likely to appreciate us going to war with the animals that decorated his shop.