The Blackthorn Key CHAPTER 1
“LET’S BUILD A CANNON,” I said.

Tom wasn’t listening. He was deep in concentration, tongue pinched between his teeth, as he steeled himself for combat with the stuffed black bear that ruled the front corner of my master’s shop. Tom stripped off his linen shirt and flung it heroically across the antimony cups gleaming on the display table near the fire. From the oak shelf nearest to him, he snatched the glazed lid of an apothecary jar—Blackthorn’s Wart-Be-Gone, according to the scrawl on the label—and held it on guard, a miniature ceramic shield. In his right hand, the rolling pin wobbled threateningly.

Tom Bailey, son of William the Baker, was the finest fake soldier I’d ever seen. Though only two months older than me, he was already a foot taller, and built like a blacksmith, albeit a slightly pudgy one, due to a steady pilfering of his father’s pies. And in the safety of my master’s shop, away from the horrors of battle like death, pain, or even a mild scolding, Tom’s courage held no equal.

He glared at the inanimate bear. The floorboards creaked as he stepped within range of its wickedly curved claws. Tom shoved the curio cabinet aside, making the brass balances jingle. Then he hoisted his flour-dusted club in salute. The frozen beast roared back silently, inch-long teeth promising death. Or several minutes of tedious polishing, at least.

I sat on the counter at the back, legs dangling, and clicked leather heels against the carved cedar. I could be patient. You had to be, sometimes, with Tom, whose mind worked as it pleased.

“Think you can steal my sheep, Mr. Bear?” he said. “I’ll give you no quarter this day.” Suddenly, he stopped, rolling pin held outward in midlunge. I could almost see the clockwork cranking between his ears. “Wait. What?” He looked back at me, puzzled. “What did you say?”

“Let’s build a cannon,” I said.

“What does that mean?”

“Just what you think it means. You and me. Build a cannon. You know.” I spread my hands. “Boom?”

Tom frowned. “We can’t do that.”

“Why not?”

“Because people can’t just build cannons, Christopher.” He said it like he was explaining why you shouldn’t eat fire to a small, dull child.

“But that’s where cannons come from,” I said. “People build them. You think God sends cannons down from heaven for Lent?”

“You know what I mean.”

I folded my arms. “I don’t understand why you’re not more excited about this.”

“Maybe that’s because you’re never the one on the pointy end of your schemes.”

“What schemes? I don’t have any schemes.”

“I spent all night throwing up that ‘strength potion’ you invented,” he said.

He did look a little dark under the eyes today. “Ah. Yes. Sorry.” I winced. “I think I put in too much black snail. It needed less snail.”

“What it needed was less Tom.”

“Don’t be such a baby,” I said. “Vomiting is good for you, anyway. It balances the humors.”

“I like my humors the way they are,” he said.

“But I have a recipe this time.” I grabbed the parchment I’d leaned against the coin scales on the countertop and waved it at him. “A real one. From Master Benedict.”

“How can a cannon have a recipe?”

“Not the whole cannon. Just the gunpowder.”

Tom got very still. He scanned the jars around him, as if among the hundreds of potions, herbs, and powders that ringed the shop was a remedy that would somehow get him out of this. “That’s illegal.”

“Knowing a recipe isn’t illegal,” I said.

“Making it is.”

That was true. Only masters, and only those with a royal charter, were allowed to mix gunpowder. I was a long way from either.

“And Lord Ashcombe is on the streets today,” Tom said.

Now that made me pause. “You saw him?”

Tom nodded. “On Cheapside, after church. He had two of the King’s Men with him.”

“What’d he look like?”

“Mean.”

“Mean” was exactly what I’d imagined. Lord Richard Ashcombe, Baron of Chillingham, was King Charles’s loyal general, and His Majesty’s Warden here in London. He was in the city hunting for a pack of killers. In the past four months, five men had been butchered in their homes. Each of them had been tied up, tortured, then slit open at the stomach and left to bleed to death.

Three of the victims had been apothecaries, a fact that had me seeing assassins in the shadows every night. No one was sure what the killers wanted, but sending in Lord Ashcombe meant the king was serious about stopping them. Lord Ashcombe had a reputation for getting rid of men hostile to the Crown—usually by sticking their heads on pikes in the public square.

Still, we didn’t need to be that cautious. “Lord Ashcombe’s not coming here,” I said, as much to myself as to Tom. “We haven’t killed anyone. And the King’s Warden isn’t likely to stop by for a suppository, is he?”

“What about your master?” Tom said.

“He doesn’t need a suppository.”

Tom made a face. “I mean, isn’t he coming back? It’s getting close to dinnertime.” He said “dinnertime” with a certain wistfulness.

“Master Benedict just bought the new edition of Culpeper’s herbal,” I said. “He’s at the coffeehouse with Hugh. They’ll be gone for ages.”

Tom pressed his ceramic shield to his chest. “This is a bad idea.”

I hopped down from the counter and grinned.

• • •

To be an apothecary, you must understand this: The recipe is everything.

It isn’t like baking a cake. The potions, creams, jellies, and powders Master Benedict made—with my help—required an incredibly delicate touch. A spoonful too little niter, a pinch too much aniseed, and your brilliant new remedy for dropsy would congeal instead into worthless green goo.

But new recipes didn’t fall from the sky. You had to discover them. This took weeks, months, even years of hard work. It cost a fortune, too: ingredients, apparatus, coal to stoke the fire, ice to chill the bath. Most of all, it was dangerous. Blazing fires. Molten metals. Elixirs that smelled sweet but ate away your insides. Tinctures that looked as harmless as water but threw off deadly, invisible fumes. With each new experiment, you gambled with your life. So a working formula was better than gold.

If you could read it.

?M08?

02160911101825261310092611221315240322132410220710092611221315141607011613010417261122131514142207151126152613021304092514261122132215260720080419

Tom scratched his cheek. “I thought there’d be more words and things.”

“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.

“What about that?” I said. Hanging from the ceiling near the fireplace was a small iron cauldron. “We can shoot at the bottom of it.”

Tom pushed aside the antimony cups on the other table, leaving enough space to put down the cauldron. I picked up our cannon and pressed it against my abdomen to hold it steady. Tom tore a scrap of parchment from our deciphered recipe and held it in the fire until it caught. Then he lit the cannon’s wick. Sparks fizzed, racing toward the pipe like a flaming hornet. Tom dived behind the counter and peeked over the top.

“Watch this,” I said.

The blast nearly blew my ears off. I saw a burst of flame, and a mound of smoke, then the pipe kicked back like an angry ox and nailed me right between the legs.