The tall boy nodded. He was very thin with spiky hair and bluish shadows under his eyes. He coughed.

"Hello," said Flavia. "We're studying how bread is made and Porcius has been showing us around."

"That's my boy!" Pistor hooked his arm round Porcius' neck and gave his son an affectionate squeeze. "He and Ericius here are going to take over the business one day." Porcius squirmed free of his father's hairy arm, but Pistor didn't seem to mind. "Any questions you'd like to ask me about the baking process?"

"How many slaves do you have?" Flavia asked.

"Just the two," said Pistor. "The one we call Teneme and the one by the ovens there: his name is Tertius. He's also our accountant. This is a family business. Quality not quantity. Special loaves, mainly. Some pastries. Our famous poppy-seed rolls. Panis popularis for our preferred customers. The slaves do the milling and kneading and baking. I supervise. My family and I sell at the counter."

Ericius coughed again, and Pistor slapped his tall son on the back. "Both my boys do the early shift, before they go to school. Then my daughter Titia takes over."

"You said some bread has been going missing?" said Flavia.

Pistor nodded. "That's been going on for months. At first the amount of disappearing bread was so small that I didn't notice. But I've been keeping strict accounts for the last few weeks and just this morning I calculated that it's almost always a dozen of my special poppy-seed rolls that go missing."

"That's not very much," said Jonathan.

"No, it's not," he scowled. "But it doesn't matter if it's one roll or a hundred. There's a thief in my household. That's what matters." He spat onto the floor. "And you know, it's very strange. The thefts only occur every seventh day."

"Every seventh day," said Flavia to the others as they walked back home. "I know every eighth day we have the nundinae: the market days. But why every seventh day?"

"The Sabbath!" said Jonathan.

"Tomorrow's the Sabbath, isn't it?" said Flavia.

"Actually it starts this evening," said Jonathan. "You Romans start the day from sunrise. For us Jews, the day begins at sunset."

"It's good you're Jewish and Aristo lets us off lessons on the Sabbath," said Flavia. "That means we have a free day tomorrow. I think each one of us should follow a member of Pistor's household tomorrow and see where they go."

They all nodded.

"Lupus, you follow the boys to school. And Nubia, you keep an eye on Titia or Fausta, whoever comes out first. Take Caudex as your bodyguard. Jonathan and I will hang around the bakery and see if Pistor or the slaves go anywhere."

"Who'll be your bodyguard?" asked Jonathan. "You know your father doesn't like you going out alone."

"I'll take Scuto," said Flavia, and then muttered under her breath. "But you'd better not tell pater."

Early the next morning, just before dawn, the four friends stood watching Pistor's bakery from across the street. The bakery window was a bright square of yellow where a line of hanging oil lamps illuminated Pistor and his two sons. They were already selling bread to a steady stream of customers. Beyond them Flavia could see the slave called Tertius taking bread out of the ovens.

"Look at Pistor," muttered Jonathan. "Porcius and Ericius could eat a whole loaf each and he wouldn't notice."

Titus Nasenius Pistor was resting his forearms on the counter and gossiping with his customers. His two sons were doing most of the work, handing out bread and taking coins. Flavia's door-slave Caudex and her old nurse Alma were among those in the queue. This was their daily routine.

Flavia had rarely been out of the house this early and she was surprised to see how busy it was just before dawn. It was chilly and she could smell the smoke from the torches people held.

She shivered and pulled her woollen palla tighter round her shoulders. Her bare legs were cold, too, so she stood closer to Scuto and let the heat from his furry body warm her calves. He looked up at her, and gave his tail a tentative wag. When Flavia shook her head at him he sighed and lay down on the pavement. Flavia didn't mind: now his body was warming her feet.

Presently Alma stood silhouetted in front of the bright rectangle above the bakery counter. She chatted with Pistor for a few minutes and finally followed the torch-bearing Caudex back across the street to Flavia.

Alma smiled and handed out bread rolls. "There you go, my dears," she said. "Try those."

"Behold!" said Nubia. "They are warm."

Jonathan bit into his. "And delicious!"

Flavia gave half her warm roll to Scuto, who was on his feet again. He devoured it in one gulp and kept his eyes fixed on her face.

Lupus chomped his roll carefully with his molars, then tipped his head back to swallow. He had no tongue and every bite of food threatened to choke him.

"Do you want us to stay with you here, dear?" Alma asked Flavia. "Caudex and I usually go to the meat market next."

"You can carry on shopping," said Flavia. "But can we keep Caudex?"

The four friends - plus Scuto and Caudex - had moved further up the road to a place from which they could see anyone coming out the back door of the bakery. The sky was pale in the east when two dark shapes emerged from this door and moved towards the forum.

"There go the boys, Lupus," whispered Flavia. "Follow them!"

Lupus nodded and disappeared after Porcius and Ericius.

A moment later Flavia jumped as the shutter of the caupona behind them rattled open. She turned to see a sleepy-looking man in a pale tunic yawning at them.

"You waiting for me to open? Have a seat and I'll be with you in a moment."

"We may as well," whispered Flavia to the others. "If we sit here and have a cup of hot spiced wine, we'll be less conspicuous."

"Behold," said Nubia, as they sat at a rickety table near the marble bar. "Pistor's wife and daughter are now serving bread."

"And he's still busy chatting to his friends," snorted Flavia.

There was no longer a queue outside the bakery, but a steady trickle of customers still came and went.

Flavia and her friends had drunk two beakers of hot spiced wine - well-watered - before Titia disappeared from the bakery counter and reappeared a few minutes later at the back door.

"There goes Tidal" said Flavia with satisfaction. "Nubia, you and Caudex follow her. And don't let her spot you. She knows who you are."

It was mid-morning, and Jonathan's stomach was growling. He had only eaten one bread roll and drunk some weak spiced wine. He and Flavia sat at the table, warming their feet beneath Scuto's furry stomach.

"I'm hungry," Jonathan remarked. "It seems like I'm always hungry these days."

"Here." Flavia grinned at him and pushed a silver coin across the table. "Buy us a couple of their rolls. We'll see how good they are."

"Not as good as Pistor's," said Jonathan a moment later. He chewed his roll and suddenly he winced. "Ow!" He reached into his mouth and pulled something out.

"What is it?" asked Flavia, her grey eyes wide.

"Bit of grit. I could have broken a tooth. No," he said, "these rolls are definitely not up to Pistor's standards."

"I'm bored," sighed Flavia. She rested her elbows on the table and her chin in her hands. "I guess being a detective involves a lot of waiting. I wish I had a scroll. But if I was reading then I couldn't watch the bakery doorway."

"Shall I recite some poetry for you?" asked Jonathan. "I know lots of it. It's from the Tanak."

"What's the Tanak?" asked Flavia.

"Our Holy Book," said Jonathan. "The T stands for 'torah', the first five scrolls. The N stands for 'nevee'eem' which means 'prophets'. And the K stands for 'k'tooveem' which means the 'writings'. When you add vowels you get the word Tanak, our holy writings."

"And there are some poems?" asked Flavia.

"There are a hundred and fifty, which we call psalms. I can recite them all. Choose a number."

"What?"

"Choose a number between one and one hundred and fifty." "Um . . . a hundred . . . and four!" said Flavia.

"O Lord my God, you are very great," recited Jonathan, "You are clothed in glory and majesty and you wrap yourself in light like a garment. You stretch out your heavens like a tent and you make the clouds your chariot . . ."

"Jonathan, that's beautiful," said Flavia. "I never knew you could do that."

"I know all the psalms by heart," said Jonathan proudly. "Choose another number and I'll see if I can tell you the last line. That's a bit harder . . ." He laughed at the expression on her face. "Go on," he said. "Test me."

"OK. Sixty-seven. What's the last line of poem sixty-seven?"

"That's a short psalm; only seven verses. I'll tell you the last two lines . . ." He paused for a moment, then looked up and to his left, " 'The earth will yield its harvest and God our God - will bless us. God will bless us, so let all the ends of the earth be in awe of him.' "

"Teach me!" cried Flavia. "Teach me a psalm!"

"I'll teach you one of our prayers," said Jonathan, "the one our Messiah taught us: Pater noster, our father . . ."

"Pater noster," repeated Flavia, and then she pointed: "There goes the runaway slave!"

"What?"

"Teneme. Look how fast he's moving! Quick, Jonathan. Follow him!"

"Good morning, sir," said Flavia casually, and leaned on the cold marble counter of the bakery. "May I try another one of your poppy-seed rolls?"

"Of course," said Pistor. "That will be one as. Still working on your project?" he asked, as he slid her change across the counter.

She nodded.

"Then why don't you come on in?"

"Can my dog Scuto come in, too?"

Pistor nodded.

A moment later, Flavia and her dog entered the bakery. It was almost deserted. Apart from Pistor, there was only a slave sitting at a table in a corner.

Pistor had just turned to serve a customer, so Flavia wandered over to the table. Scuto followed her, his toenails tapping on the brick floor. He sniffed the slave's knees and wagged his tail.

The fair-haired slave stopped flicking beads on his abacus and reached down to scratch Scuto behind the ear.

"You're Tertius, aren't you?" said Flavia.

He nodded.

Flavia casually ran her finger over some letters carved into the smooth wooden surface of his small table. "Do you keep all the accounts?"

"I used to," sighed Tertius, picking up his quill pen and making a note on a piece of papyrus. "But now the master insists on going over them. And sometimes he does spot checks. He has to account for every loaf or roll produced. We even have to note how many rolls are burnt in the ovens."

"Why?" asked Flavia. "Why is he so careful?"

Tertius lowered his pen and his voice. "They say his wife's grandmother was the cause of a famine in Ostia, in the days of the Emperor Augustus."

"Really?"

Tertius nodded. "Her name was Fausta, too. When she had quadruplets, the soothsayers were terrified and predicted four years of famine."

"I remember!" cried Flavia. "Didn't Admiral Pliny tell that story in his Natural History?"

"You're very well-read," said Tertius. "And do you remember what happened? Was the prophecy fulfilled?"

"It turned out that the famine only lasted four days?"

"Correct," said Tertius. "But ever since, Fausta's branch of the family has been obsessed with keeping records. She makes him do it, in case there is ever another famine and they are accused of wasting grain."

"I see," breathed Flavia. Then she frowned. "What's this?" she said, running her finger over the inscription in the table.

Tertius flushed. "Oh, that. It's just a game. Like a puzzle."

Flavia turned her head. "What does it say? The sower . . . holds . . . the works?"

SATOR.

AREPO.

TENET.

OPERA.

ROTAS.

"It says 'The sower, Arepo, holds the wheels at work.' " "What does that mean?"

"It doesn't really mean anything. But if you write it out . . ." He opened a wax tablet, turned it sideways and wrote in tiny neat letters: SATORAREPOTENETOPERAROTAS.

"It reads the same backwards as it does forwards," said Tertius.

"Oh!" Flavia hopped with excitement. "I know those kind of codes. They have a special name. It's called a . . . a . . ." "Palindrome," said Tertius.