The Blackthorn Key (6 page)

“What is it?” he said.

“Our universe. The Sun, and the Earth, and the other five planets. Each big circle represents an orbit.”

“Oh. Oh, I see, they go around.” He traced a finger over the figure in the center. “Why does the Earth have these peaks? Are they mountains?”

“That's not the Earth,” I said. “That's the Sun.”

“Why is the Sun in the center?”

“Because that's where the Sun is.”

“It is?” Tom frowned. “Says who?”

“This man.” I handed him the book.

He squinted at the cover. “
Sys
 . . .
System
 . . . What is this?”

“
Systema cosmicum
,” I said. “It's Latin. It means ‘cosmic
system.' It says the Sun is at the center of the universe and all the planets go around it.”

Tom flipped through it, a skeptical expression on his face, until he got to the title page. “By Galileo Galilei. Sounds Catholic to me,” he said disapprovingly.

“Just . . . that's what the figure is, all right? The Sun is at the center, and the six planets go around it. Mercury's the closest, then Venus, then Earth—see, this circle on the third ring is us—then Mars, Jupiter, and Saturn. That's all of them.”

He turned the cube over. “So what are the rest of these symbols?”

“They're the planets.” I pulled out a sheet of parchment that had been slipped inside the back cover of the book, inked with Master Benedict's smooth, familiar handwriting.

Planetary Symbols

Tom looked from the parchment to the cube.

“But there's only five symbols here,” he said. “There's Jupiter, and Venus, Saturn, Earth . . . Mars. Mercury's missing.”

“Right,” I said. “Now look at the top again. The first circle, closest to the Sun. The black dot on it, where Mercury's supposed to be.”

He peered at it. “Oh! It's a hole.”

“I think that's where the key goes. And the missing symbol is the clue.” I pointed at the shelf behind us. On it was a ceramic jar, smaller than its neighbors. “Can you bring that down?”

Tom rose obligingly and grabbed the jar one handed. He looked surprised. “It's heavy.”

I took an empty cup from the rack behind the counter, then unstoppered the jar. “This,” I said, “is quicksilver.”

I tipped the jar over the cup, draining it carefully. A shiny silver liquid poured out.

Tom was amazed. “How did you melt that?”

“It's already melted. It's not hot.” I dipped my finger in it. “Look, you can touch it.”

Cautiously, Tom held out a finger. He barely grazed the surface, then pulled away, leaving jittering waves that stilled almost immediately. He tried again, going deeper. “Strange. It doesn't really feel like anything. It's almost like it's not even there. What's it for?”

“Treating diseases. Really bad ones, that you get on your . . . you know. But what we want it for is . . . the key!” I turned the jar over.

Nothing happened.

“Do I applaud now?” Tom said.

I looked into the jar, frowning. “There's nothing in here.”

“Why did you think there would be?”

“Because mercury is supposed to be the key.” I jiggled the cup, trying to see if anything had slipped out with the liquid. “That's what quicksilver's real name is. It's called mercury. And that hole is where the planet Mercury would be.”

“That's clever,” Tom said, looking at the cube, “but I don't see how you're going to get a key in here. The hole is too small. And it's round. There's no such thing as a round key.”

He was right. A round key didn't make sense; it wouldn't have any teeth. But Master Benedict had promised there was a key, and it was in this room.

That's when it struck me. “Tom! You're a genius.”

“I am?”

I pointed at the hole. “How would you get a key in there?”

“I told you, you can't. It's too small. You'd need something that could slip inside . . .” His eyes widened as I swirled the cup, sloshing the mercury around. “A
liquid
key? How is that even possible?”

“Let's find out.”

He held the cube steady. Carefully, I tipped the cup. Three drips of liquid metal splashed onto the surface, running along the engraved circles like little silver beads. They drained toward the hole and slipped inside. Still, nothing happened.

“Maybe you need more,” Tom said.

I poured again, and a third time.

Click
.

The seam around the top opened. Just a crack.

Slowly, I lifted the lid. I looked inside.

I gasped.

TOM LEANED OVER. “WHAT IS
it? What is it?”

I pulled it out and placed it on the counter.

It was a coin, shiny silver. Real silver.

Tom's eyes bulged. “A
shilling
. You got a
shilling
.”

A shilling. Twelve whole pennies. I was
rich
.

The coin was brand new, the center stamped with a profile of the king. Around it was inscribed
CAROLUS II DEI GRATIA
. Charles II, by the grace of God. Oak Apple Day, his coronation day, his birthday. And mine.

I felt like I was glowing.

Tom picked up the shilling, marveling at it. I peered
into the puzzle cube again. “Look at this,” I said.

The inside of the cube was antimony, too, except for one face opposite the hinge. Here it was glass, letting us see the lock's mechanism. A channel from the top guided the quicksilver into a well in the front, where there was a lever. When we'd poured enough in, its weight pushed the lever down, which opened the latch.

“Brilliant,” Tom said.

It was, even more than it appeared. Master Benedict loved hiding things inside other things. Codes within codes, puzzles over locks. Here, too: inside my birthday gift, a second present. And beneath it all, a lesson in symbols.