“Remember the murals?” Joon called over his shoulder as he biked up the street. Rachel followed close behind him. “All the important scenes in Setauket history, right?”
“Right,” she called back.
“Well, I was thinking about the clue, and what stones were in the murals.”
“We already tried both of them.” She’d happily turn over every rock in town, but she wasn’t certain that the clue led to an ordinary rock. If Nancy was a spy, if she’d left this puzzle, then the clue would be more clever than that. She thought about how Nancy had been constantly underestimated, first by those around her, then by some historians. I’m not going to underestimate her. “I don’t know if we’re looking for an actual rock.”
“That’s just it: the clue isn’t rock. It’s stone.”
“Literally the same thing.” Her bike bounced over a crack in the sidewalk, but she kept it steady.
“But both Patriots Rock and the Devil’s Rock are specifically called rocks, whereas there is an important stone in the murals that’s actually called a stone. Okay, it’s not actually shown in the murals, but you know it’s there.”
“What do you mean?” she asked. “Also, did you just use the word ‘whereas’?”
“In the murals, along with the picture of the blacksmith and the shipbuilding, there was a picture of a mill.” He halted at the stop sign in front of a crosswalk. The Setauket Post Office, a tiny building that looked like a Greek temple with a golden eagle on its peak, sat across the street. Beyond it was Frank Melville Park.
“I remember.” She didn’t actually. But she wanted to keep him talking.
“You know how I did my social studies project on grist mills? Well, I remembered that while we were touring the house and my parents were trying to pretend they would be fine with my dad having a two-hour commute each way, even though I could tell that they’re not—they don’t want to move any more than I do, but they don’t see another option. Just not enough houses to rent here.”
“Two hours!” She nearly fell off her bike. Catching herself with her foot, she steadied the bike. She must have misheard. Two hours? There was no chance he’d stay in the same school district if he was that far away. And how often would Mom agree to drive her to visit? “What, is it in New Jersey?”
“Not the point, Rachel,” Joon said as they crossed the street.
“What is the point?”
“The Setauket Grist Mill was used to grind wheat into flour, which made it an essential part of the community—that’s totally what I wrote on my diorama. Anyway, everyone used the mill, which means so did Anna Smith Strong.” Passing the post office, he aimed for the paved path that led around the pond. “And do you know what the mill used to grind their wheat?”
Rachel veered around a man walking a terrier. “What?” she called to Joon.
“A millstone!”
That . . . was possible.
Framed by leaves, the Mill Pond peeked at them between the trees. She glimpsed a bridge with three low arches on the opposite end. The mill had been built beside it, and she caught a quick glimpse of its wheel before it was blocked by green. They biked between bushes. On the grass beside the path, a rabbit froze, watching them, then fled into the ivy and ferns. They passed a large, leafless tree with dozens of names and initials and hearts carved into its bark. Beneath it, a family of swans preened themselves. Six baby swans with downy gray feathers waddled on the shore. One of the parent swans lifted its curved neck to watch Rachel and Joon bike by.
“I’ve been thinking about how too,” Joon said, “how she could have left a clue on a millstone. You saw the size of her gravestone. Hers and her husband’s were the biggest in the entire cemetery. So her family must have had money. What if she paid the miller to let her leave a clue on the millstone?”
“She wouldn’t have even had to tell the miller why,” Rachel said. “She could have just pretended to be a nice, eccentric old lady with money to spare.”
“Yeah, rich people do weird stuff all the time.”
“Or maybe she did tell him part of the truth: she wanted to leave a puzzle for someone to find. She wanted someone to see her.” Someone like us, she thought.
“All we have to do is find the millstone and figure out the next clue.”
Ahead she saw a red barn and a community garden. Another rabbit munched on the grass just outside the vegetable garden. As they rounded the corner, she saw it clearly for the first time: the mill beside the bridge.
She slowed, braking, and they both dropped their bikes on the grass.
The mill was covered in gray shingles with white trim and green shutters. A sloped roof dipped down into the bushes on one side, and a wooden waterwheel was fixed to the other side. It disappeared into the reeds and didn’t turn.
Rachel and Joon rushed to the nearest window and peered in, but they saw only black plywood. “It’s boarded up on the inside,” Joon said.
The front door was white, with painted glass above it—a scene of the bay, with chickadees perched on the branches of a tree in the foreground. Rachel pulled on the door and wasn’t surprised that it was locked. She stepped back. “How do we get in?”
“Maybe there are hours it’s open to the public?” Joon plucked a brochure out of the covered box staked into the ground near the door. He unfolded it. As he read, his face fell, and his shoulders sagged.
“Not open?” Rachel guessed.
“Not real.”
“What do you mean?” It was right in front of them. Quaint. Cute. With a waterwheel. Granted, the wheel wasn’t moving, but it’s not like anyone needed flour ground up while they walked their dog around the pond.
He shoved the brochure in front of her face. “It’s a reproduction. Built in 1937 to look like the mills in the area, it says. The real mill used to be near here—that must be the one in the school mural, the one that Anna Smith Strong used—but it was torn down to make the park.”
“Oh.”
“The clues have been lost,” Joon said, deflated. “Really, I shouldn’t be so surprised. Did I really think we’d find clues left centuries ago?”
It was a lot of time. But Nancy had to have known that her clues would need to last if she wanted them discovered after her death. Wouldn’t she have planned for that? On the other hand, how could she have known the mill that everyone used would be torn down for a park? Maybe she thought her daughter would find the clues just a few years later. Or her granddaughter. She couldn’t have guessed her mystery would sit unsolved for over two centuries.
Rachel took the brochure. It had a photo of the mill, the bridge, and the swans. Even the post office was a reproduction, it said, in Greek revival style, whatever that meant. She sighed, lowering the brochure, staring at the ground.
Her eyes widened.
“Joon?” she said.
“I’m going to have to move away, and that’s that. Our last adventure is ending in failure. I was so sure I’d thought of the answer—”
“Joon.”
“Yeah, I knew it was unlikely but worth a try, I thought. Guess I got my hopes up because it was easier than—”
“Look down.”
They were standing on a stone about three feet in diameter. Shaped like a flat doughnut, it had a fist-sized hole in the center that was filled with dirt and tufts of grass. Grooves striped the stone, dividing it into narrow pizza slices. A second stone was embedded in the ground next to it. The post for the brochure holder was driven into its center.
Joon knelt. “Millstones.”
“They look worn—old,” Rachel said.
“They must be the original millstones,” Joon marveled. “They used them as a walkway. Quick, look for anything unusual.”
Rachel squatted next to him, and they began clearing the dirt from the grooves and around the edges. She yanked out grass and ran her fingers through the grooves. “I’ve never seen a millstone before. How do we tell what’s unusual?”
Joon pulled a ruler out of his backpack and began using it to clean the grooves. He told her about grist mills, reciting facts from his poster. The mills were powered by water. You put grain between the millstones, and they turned in opposite directions and crushed the grain into flour. The millstones were thick stone disks with grooves in them. At some point, someone had pried them off their gears and embedded them in the dirt here.
What kind of clue could Nancy have left that she would be sure would survive? Maybe something to do with how many grooves there were? Or what direction they pointed?
“There’s a number on this one,” Joon said.
Rachel scooted over to look as he cleared dirt from the edge. A number had been carved deeply into the stone between the grooves. “‘Six hundred thirty-three,’” she read.
“That doesn’t mean anything. Are there any words? Like on the grave marker?”
They cleared the entire top of the disk, working diligently. Dirt was stuck under all her fingernails, even the super-short ones that she’d torn off when she decided they were too annoying. When nothing else showed up, they cleared the second millstone too. It had nothing, not even a number.
“Six-three-three,” Rachel mused. “It could be a time of day. Six thirty-three in the morning or six thirty-three in the evening.” Sunrise or sunsetish, depending on the season.
“Or an address?” Joon suggested. “But then we’d need a street name.”
“I don’t even know if houses were numbered then. When did houses start being numbered? Anyway, I don’t think there were enough houses back then for there to be a house number six hundred thirty-three.”
“It could mean this stone was used to mill six hundred thirty-three pounds of flour,” Joon said. “Or it’s the six hundred thirty-third stone from wherever it’s from.”
“Do mills normally number their stones?” Rachel asked.
“Not in my diorama,” he said. “No idea if they did in real life.”
The other stone didn’t have a number. It was just this one, which made it special. Of course, Joon was right—they had no way of knowing if the number had anything to do with Nancy. Lots of things were numbered for lots of reasons.
He plopped down on the grass. “Maybe we should have stuck to looking for pirate treasure, like in third grade. Six-three-three doesn’t mean anything. If it is a code, we can’t decipher it without knowing how it was made. We need a decoder. Or—”
“Or a codebook?” she suggested.
“Yeah, exactly.”
She felt that familiar fizzing feeling, bubbling up inside her. She’d just seen lots of codes in a very special codebook. Lots of three-numbered codes.
For example, 711 was George Washington.
And 355 might have been Anna Smith Strong.
So, what was 633?