Snow and Rose tried to find their way back to the Underground House again, but they grew tired of looking. They listened for the music with their ears close to the ground, but there was only the quiet chirp and rustle of the forest. They sifted through leaves, staining their dresses with moss, but couldn’t find a trace of a windowpane or hinge.

Snow drifted back to the hillside, back to watch the old house. They started to return to their routines from the first weeks in the cottage. The only difference was that once or twice Rose saw Snow fish out the key from the library and look at it, waiting for it to do something.

But soon there was a new nip in the air, and everything began to look different as the beginning of autumn set in. One morning, after a breakfast of warm oats and milk, their mother disappeared into her room and reappeared with two bundles. Snow’s bundle was a cardigan the color of a sparrow’s egg. Rose’s was a pullover stitched from yarn the color of red winterberries.

Wrapped in their new sweaters, Snow and Rose felt inspired to go off in search of the Underground House one more time. The woods were sun-dappled as the girls hopped over the stream. On the other side, a frog two sizes too big stared out at them with eyes like black marbles. Snow and Rose looked at each other, then hurried past the old-man grove and on to the clearing.

Today, the sisters covered different patches, walking carefully, feeling for hidden clues beneath their feet for what felt like the hundredth time.

They found nothing. They traced their steps the way the wolves had chased them, circled back to the stream, and followed the water. “Maybe it was never there,” Rose said. She pulled her sweater sleeves down over her thumbs to warm her hands. “Maybe—”

Snow stopped suddenly. “Wait!” she called out. She held her finger to her lips and looked at Rose. They had come to a new place, where the woods were deeply shadowed.

Snow and Rose waded into a sea of ferns so dense they couldn’t see their feet below. “Maidenhair and staghorn and—” Rose recited quietly to herself, making notes as the ferns brushed her legs.

“Shhh!” Snow hushed her. “I hear it!”

Rose strained her ears. “I don’t hear anything.”

Snow led her farther through the ferns that swayed above their knees.

Rose could hear the music now, faint in the crisp, chilly air.

“Look for a door in the ground,” Rose reminded Snow, though she needed no reminding. They followed the music to a tree. It was circled in roots that curled in and out of the ground in arches big enough to crawl through.

All of a sudden, the music seemed much closer.

Snow went down on her hands and knees to crawl into the roots, until only the bottom halves of her legs were above the ground. Then she scooted backward and looked up, her face smudged with dirt.

“This is it!” Snow said, jittery with excitement. “There’s a tunnel under this tree.”

Rose’s fingers started to worry. She looked at Snow.

“I’ll go first,” Snow said. In a blink, she dove back in. Rose heard her muffled voice—“Are you behind me?”—before the last of Snow’s boot vanished from sight.

Rose breathed in. She worried about what was beyond the tunnel. Then she had to stop thinking, because Snow was gone. “Yes,” Rose called back, and crawled in after her.

The tunnel was dark and winding: a small labyrinth under the tree, knotted and bumped, hung overhead with tendrils. A blue-green glow came up through the root walls as they followed the music, crawling down through a thousand years of growing.

Suddenly, there was a steep drop where the tunnel gave way to nothing. Snow slid forward, and Rose tumbled after her. They landed with two bumps.

“Crumbs,” Snow muttered. She looked up, blinking slowly. Rose grabbed her satchel and rubbed her sore knees. She looked around, trying to get her bearings.

The music had stopped. They were in a cavern, an underground room. The walls glowed faintly in the blue-green light, and all around them was the smell of earth.

A warm yellow light appeared from around a bend. A lantern came into view, just before the person carrying it.

“Who are you, then?” the boy asked. His voice was gentle and lifted up at the end.

The boy’s face was pale, with dark eyes and a snarl of brown hair. The rest of him was spindly. It was hard to tell how old he was: he was about as tall as Rose, but skinnier than either of the sisters. He wore a moth-eaten sweater that might’ve once been white and a pair of patched brown trousers. The beginning of a smile played at the corners of his mouth.

The girls stood and brushed themselves off.

“Who are you?” Rose said, fixing her hair and brushing leaves from Snow’s back.

The boy laughed, one of those half-finished laughs that barely escape, as Snow untangled a length of root from her hair.

Snow shot him a look. “Yes, who are you?”

“Ibo,” he said. The boy took a handkerchief from his pocket and blew his nose.

“Bebo?” Snow said, laughing.

His cheeks grew rosy in the lantern light. “Ivo, I said. I-V-O.” The boy shifted his feet. “Anyway, you’re the ones who tumbled into my farm. What are your names?”

“I’m Rose, and she’s Snow.” Rose hoped she sounded friendly enough to make up for Snow. “Um…how do you do?”

“People who’ve got strange names shouldn’t throw stones,” Ivo said, shooting a look at Snow. He fidgeted, and both girls noticed that, instead of gloves, he wore on his hands a pair of old woolen socks, cut off at the toes. “You don’t look like you’re from here, then,” he added, glancing at the delicate embroidery stitched into the hems of their dresses.

“Well, that’s because we’re not,” Snow replied.

Rose wondered if that was still true, after all this time in the woods.

“And how’d you get to the farm?” the boy asked.

“We sort of fell,” Rose said. Ivo smiled. “We crawled into the tunnel because we heard music.”

“Do you know who plays it?” Snow asked. Her voice took on a different, excited tone.

“I do,” Ivo said, looking pleased.

The girls explained how they’d first found the chimney at the beginning of summer, how they’d been looking ever since.

Ivo’s eyes lit up. “That was the two of you, then? Pawing around the front door?” He laughed. “Oh, Mum was so worried. She hid us well after that.” The boy looked at them with serious eyes. “There are dangerous things, things that shouldn’t be…” His voice trailed off.

“Well, we’re very dangerous,” Rose joked nervously, then saw that he didn’t smile. “What things do you mean?”

“Yes, what kinds of things?” Snow repeated.

“Well, the big creatures, mostly. The Menace of the Woods, we call it,” Ivo replied.

Rose’s eyebrows knitted together. She looked sideways at Snow. She thought of the blackbird and the big wolf and the frog.

“And there are other things, things you can’t see, but you just get a feeling sometimes….” Ivo stopped when he saw the girl’s expressions. “I didn’t mean to scare you,” he said. “Just—be careful, that’s all.”

“What is this place, anyway?” Snow asked.

Ivo smiled. “I’ll show you.” He led with his lantern, and they followed him through one, two, three bends in the cavern.

“Here we are, then,” said Ivo.

There was a faint musty smell. In some places it was like barely moldy bread; in other places, like a sweater packed away in a chest and unfolded a year later. The walls were dimly lit with the same glow the sisters had seen before, and Ivo held his lantern in the center of the room, casting more light onto its contents. There were mushrooms everywhere. Tiny ones grew alongside giants, their caps glowing scarlet and pink, biscuity brown, and ghostly white in the dark of the cavern. They grew round, squat, branching, and slender. Each kind grew neatly on its own carpet of moss, rising out of the earth.

Rose put her hand to a stretch of glowing wall and looked at Ivo quizzically.

“Lantern moss. Otherwise we’d only have these,” Ivo said, swinging his lantern. “A few of the mushrooms glow a bit, like those near your head, Snow. Starlights, we call them.”

Snow turned and saw a patch of delicate white mushrooms. They seemed to reach out to her. She stretched her index finger to touch one, and when she pulled it back, the faintest luminescent dust was traced on her fingertip.

“But it’s not enough for proper light,” Ivo added.

“So what are all these mushrooms for?” Snow asked.

“All sorts of things,” Ivo replied. “Some are just for ordinary eating, some for medicine. A few, I don’t want to know who buys them.”

Rose gazed at the dark garden around her. “Do you know all their names?” she asked, her face lit with lantern moss.

“Well, I don’t know their proper names,” he said a bit sheepishly. “Only what we call them.”

Rose nodded. “So what about these?” She pointed to a blush variety.

“Dancer’s Skirts,” said Ivo.

“And these?”

Ivo and Snow came to her side, and as Rose pointed, the boy recited: “Milliner’s Thimbles, Ruby Toadstools, Flea’s Parasols, Moon Giants, Golden Pence, Butterscotch Tinies, Devil’s Buttons, Mouse’s Buttons. Come to think of it, there’s a lot with buttons in the name.”

Rose clapped her hands in appreciation. “But why is this so far from your house?”

“Well, the earth there isn’t exactly right for growing,” Ivo replied.

“But don’t you ever get scared down here by yourself?” Rose asked.

“I don’t mind it,” Ivo said. He smiled his crooked smile. “I was born in the dark.”

“What about the music?” Snow said impatiently, then added a late attempt at politeness. “Not to interrupt…”

Ivo’s eyes lit up, and he disappeared into the tunnels. While they waited, Rose stood on her tiptoes to see what grew on the highest shelves. Snow sniffed a patch of lantern moss and sneezed.

When Ivo returned, he was cradling a violin in his arms. He produced a thin bow and sat on one of the stumps scattered through the cavern for seating. Then he proceeded to play. It was the same mysterious music they’d heard in the warm summer twilight at the Underground House, and then again today.

“That’s it!” Snow said, beaming. “I play the violin, too.”

Ivo held his bow silent in midair. “This is a fiddle,” he said, his voice confident.

“I’m pretty sure it’s a violin,” Snow corrected.

“Fiddle,” Ivo said.

“Violin.”

Rose loudly cleared her throat. “We should probably be going soon.” She turned to Ivo. “How do we get back up outside? If the way down is, well, falling down.”

“Don’t you know how to fall up?” he said. “No, I’m only fooling. Don’t worry, there’s stairs.” He placed his fiddle carefully on the stump and showed them the secret way back aboveground and into the sunlight.

“Before you go, can I show you something else?” he asked.

Both Snow and Rose nodded.

Ivo’s “something else” was a single mushroom, round and deep blue, like a dark pearl made of paper. It filled Ivo’s palm as he displayed it to each of the girls in turn.

“I’ve been waiting to show this to somebody for ages,” he said. “It’s called Sandman’s Pocket. I discovered it. I named it, too,” he said proudly.

“What does it do?” Snow said, peering down at it.

“You’ll see,” he said. He scanned the ferns and the mossed tree trunks around them. “There!” He pointed to a pair of squirrels skittering a few yards away. Ivo tossed the mushroom. There was a great puff of shimmering blue smoke as it landed, breaking apart between the two squirrels.

“I forgot to say,” Ivo added, holding his nose, “it’s probably best if you don’t breathe in.”

The girls held their breath.

The squirrels froze in mid-skitter, then appeared to drop dead.

“Oh, you wicked boy!” Snow cried.

“No, they’re just asleep!” Rose exclaimed. “You said ‘Sandman’s something,’ right? So they’re only sleeping. Aren’t they?”

Ivo looked terrified.

“Aren’t they?” Rose demanded.

The squirrels lay on the ground, not moving so much as a whisker.

“Of course!” Ivo said, bewildered. “They’ll wake up. It just takes a while to wear off.” His cheeks flushed with the realization that maybe this hadn’t been his best idea. “It’s just a bit of fun. They’ll wake up good as new,” he reassured Snow. He looked at the ground. “I should have warned you.”

The girls stood over the squirrels as Ivo waited. After a few more silent minutes, the squirrels began to twitch back to life. Then they scampered up a tree and out of sight.

“So you’re not a squirrel murderer,” Snow said, still scowling.

“Just a squirrel Sandman,” Ivo said.

“We’ve never known many boys,” Rose said. “We didn’t know if that was, I don’t know, something you’d do for fun.”

“I guess I’ve never made friends with any girls.” He looked at the sisters. “There aren’t that many friends to make here, really.”

Ivo pulled his sleeves down over his sock-gloved fingers, as Rose had done earlier. Around them the nip in the air was growing sharper, sending them back to their homes, above and under the ground. They traded awkward goodbyes, and the girls started back toward the cottage but turned when they heard Ivo call out, “Hey!”

He added, “Maybe you’ll come back sometime?” His voice sounded hopeful.

He couldn’t see their faces, but Rose smiled, and Snow did, too.

“Maybe so,” Snow called back.

At dinnertime that night, their mother, who didn’t hear many reports from their wanderings, heard all about the mysterious music that had led them to a cavern underground. Snow and Rose told her about mushrooms called Mouse’s Buttons and Dancer’s Skirts, and about their new friend, Ivo, who’d been born in the dark and played the fiddle underground.