Sasha hid behind a display of glass bottles and held her breath. She made a bad spy. She was bad at being silent.

Her toes tapped. Her fingers wiggled with the desire to order the bottles just so. She groaned every time Papa made an unfunny joke to a customer of their alchemy shop.

Ms. Kozlow fussed with the clasp of her coin purse as she stood at the counter. She seemed very nervous, even though she was very elegant, thought Sasha, and must have been twenty years old at least.

Papa studied a muddy brew in a glass vial through his spectacles.

"Now, Mr. Bebbin," said Ms. Kozlow, "I don't want this ... this —"

"Potion, madam," said Papa.

"Yes, potion. I don't want this potion to give me too much luck. I only need just enough luck."

"Of course, of course," said Papa as he grated a wrinkly, old mushroom into the drink.

Sasha ran out of breath. She let out a gust of air and inhaled another. She slapped her hand over her mouth, hoping they hadn't heard her in the far corner of the shop. She ducked down below the display of bottles filled with sleep sand and squatted next to a crate of bird eggs. She paused to make sure the giant stone phoenix egg hadn't crushed the tiny, speckled quail eggs.

Ms. Kozlow went on. "I've got a lovely little place in the Village, you see. And my bonbons are selling quite well. I wouldn't want too much luck to ruin it all. I could inherit some far-off castle, for example, and then I'd have to go clean out the moat every Thursday."

"Hmm," said Papa. He was focused on measuring the ingredients.

"Or imagine if I won some sort of contest to have a pet tiger. What would I do with a tiger in my chocolate shop?"

Sasha could think of about a thousand things one could do with a tiger in a chocolate shop. She wished she could list each one for Ms. Kozlow, but she was spying on their conversation, as she always did with the customers. That meant no interrupting. She let out a sigh instead.

"No, no," said Ms. Kozlow, "I need a precise amount of luck."

Sasha sighed again. She couldn't believe how many people in the Village believed in things like potions, magic, and alchemy — including her father, of course. It was all so ... silly.

"It would help my calculations," said Papa, "if I knew what this precise amount of luck was for."

"Oh, no, no, no," said Ms. Kozlow, bringing her purse up to her chest. "It's a private matter, I'm afraid."

Sasha noticed that Ms. K wore gloves. No one else in the Downside of the Village wore gloves. Sasha guessed she was either from Upside, or she didn't have the time to get all the chocolate out from under her nails.

"Very well," said Papa, stirring the liquid with a dried stalk of mandrake root. "Then I'll need to know your exact hair color."

"I'd say 60 percent dark-chocolate brown," said Ms. K, patting her crown of braids.

"I see," said Papa. "And do you prefer a hamster or a ham bone?"

Ms. K blinked a few times. "I suppose I prefer hamsters ... but not to eat."

"Of course not," said Papa. "That would be a silly question. And when was the last time you ate a green apple?"

Ms. K thought for a moment. "Last Tuesday, at noon."

"Excellent." Papa plucked a yellow berry from a potted plant sitting on the far side of the counter and dropped it into the mixture. The potion fizzed up to the rim and made a PLIP PLOP sound. Papa seized the mandrake root and stirred the brew furiously until the liquid calmed back down. "All right then," he said. "Yes, I think so. This is exactly the amount for just enough luck." He plugged the glass vial with a cork and handed it to Ms. Kozlow.

"Why is it ... that color?" asked Ms. Kozlow, wrinkling her nose.

Sasha thought it looked like swamp water.

"I could add some strawberry jam," said Papa. "That would help the color and with the taste of dung beetle."

Ms. Kozlow held the potion bottle with two fingers as Papa looked around his messy shelves.

Finally, he turned around and said, "I've got good news and bad news. I found the jar of jam. Unfortunately, it's empty."

He held up the jar that Sasha had finished that morning.

Ms. Kozlow frowned. "What terrible luck. It looks like I came to you just in time." Ms. K gave Papa a few coins from her purse. Then she pulled out two chocolate bonbons and placed them on the counter. "One for you, and one for your daughter," she said. "Thank you, Mr. Bebbin. You've saved my life."

Papa blushed.

From behind the display shelf, Sasha wanted to shout, Don't take it! Have some sense, woman! It's not safe! There was no telling what someone would do if they thought they were magically lucky. What if Ms. K jumped off a barn thinking she might be lucky enough to land on a passing sheep?

The door swung shut behind the chocolate maker, and Sasha was about to stand up when a head suddenly appeared over her.

"You can come out now," Papa said as he wiped down the counter. "You need to get better at sneaking, if you're going to spy on our customers."

Sasha sprang from her hiding spot, feeling a bit childish. She smoothed her tunic and straightened her shoulders. Another sale was another disaster waiting to happen. Sasha much preferred the customers who bought fancy eggs for decorating or milk from Cordelia, their dairy cow. Papa was a respectable apothecary and had a wondrous garden of strange plants that could help sick people get better. But whenever he used them for his crazy potions, Sasha was fear-stricken and furious at the same time.

Customers like Ms. K, who believed in all that hocus-pocus, were bound to be disappointed. Potions didn't work — at least, not Papa's potions. Sasha had a vague memory that her mother was the alchemist of the family, and maybe her potions had worked, but that was a long time ago. These days, it was Papa working from her mother's recipe books, and Sasha wasn't convinced. She was certain the magic was gone.

And soon, the few customers they had would complain. But Papa would insist that his calculations were correct. And then they would take Papa to the constable. And the constable would make Papa pay a huge fine for lying. And Papa wouldn't be able to pay it. And then she and Papa would go bankrupt. And then Vadim Gentry would buy up their store. And then they would be homeless. And then they would wander the countryside in poverty.

And when Mother returned from her long journey, she would never find them.

It had happened to a potion-maker in Sandtown last summer and in Rozny the year before. Papa needed to be more careful.

Sasha's heart was pounding with her runaway fears by the time she approached the counter. "Why did you promise her magic luck?"

"All luck is magic," said her father, as he poured the chalk dust he had used earlier into its porcelain container. "And I didn't promise it to her. That's simply what the potion does."

Sasha sighed and puffed her cheeks. She didn't have time to argue magic and science again. Ms. Kozlow would be walking back to the Village now, expecting some sort of extra-special luckiness.

"Of all the odds and oddity, Papa," she said in her most imposing voice, "chances are she won't get whatever she wants, and then she'll blame you. You must go to Ms. Kozlow and...