‘There must be some way out,’ Mimi said. ‘What’s the point of just sealing people inside a room?’

‘Maybe it’s a test,’ Leah said thoughtfully.

‘Or a puzzle!’ Khalid exclaimed. He pointed to the gold hieroglyphs. ‘It must be something to do with them.’

‘Oh, I bet you’re right, Khalid!’ William said excitedly. He leaned forward, his earlier alarm seemingly forgotten as his finger traced the outline of one shaped like two upright leaves. Before anyone could stop him, he prodded it. The brick sank, just like the one that had revealed the secret corridor. Mimi gasped.

Leah braced herself, expecting rocks to come crashing down on them like they had in the corridor. Khalid and George held their hands over their heads for protection. William stared at the sunken brick, his eyes wide with horror.

But nothing happened. The sound of falling debris never came.

Leah let out a relieved breath.

‘Really, William?’ Mimi demanded in disbelief. ‘Again? Haven’t you learnt your lesson yet? Stop pushing strange buttons!’

For once, William’s temper didn’t get the better of him. His cheeks flushed with embarrassment and he looked at the others apologetically. ‘Sorry,’ he mumbled. ‘I didn’t mean to.’

‘Hey, can you guys hear that?’ George said. He stared up at the ceiling. ‘It sounds like . . .’ He trailed off, his brow creased in confusion.

Leah heard it too. It was a faint hiss. It reminded Leah of the sound rice made when you poured it into the saucepan.

‘Oh no!’ Khalid groaned, pointing at the wall. ‘Look!’

A cascade of sand was pouring in through gaps in the bricks, landing on the floor in a rapidly growing heap. Leah twisted only to discover that there were similar streams of sand hissing in from all the other walls, too.

‘Was that . . . was that because I . . .?’ William trailed off. He stared at the sand in disbelief. ‘Maybe I can make it stop?’ He jabbed at the hieroglyph brick desperately. The torrent only seemed to get faster, dumping more and more sand into the room by the second.

‘William!’ Mimi shouted, her voice shrill. ‘You need to stop pressing things!’

Leah watched in horror as the sand began to form little piles that grew larger and larger as the seconds passed. Before long they would be towering dunes, filling the room with sand. If they didn’t do something, they would be buried alive!

‘We have to get out of here!’ Leah cried.

‘How?’ George blurted. ‘The doors are all sealed!’

‘We’re going to be crushed!’ Mimi wailed. She sprinted to the exit, pounding on the stone with her fists.

‘There must be a way . . .’ Leah said, as she spun around, her eyes searching for a solution. The sand was already deep enough to cover the toes of her shoes. In minutes, it would be up to her knees. They didn’t have much time. ‘Khalid, you said it might be a puzzle? What kind?’ She was speaking so fast that her words were running into each other. ‘Maybe we need to solve it to stop the sand. But we need to move fast!’

‘Um . . .’ Khalid spun, his movements frantic. He screwed up his nose as he scanned the walls, then shook his head in frustration. ‘It’s just the alphabet and some numbers! I don’t understand!’

George burst into tears. ‘We’re going to die!’

‘George, we’re not going to die,’ Leah said firmly, trying to ignore the sick feeling in her stomach as she realised that, for once, she wasn’t sure she was telling him the truth.

‘Wait!’ William suddenly exclaimed. He rushed over to where Mimi was still pounding uselessly against the door, kicking sand up into the air with every step. ‘Khalid, what’s this?’

William was pointing to three rows of hieroglyphs that Leah hadn’t noticed before. They were set out in a way that was strangely familiar. Khalid squinted as he stared at them, his lips moving as he translated the markings. ‘They’re sums, I think?’ He frowned briefly but then his face flooded with relief. ‘That’s it! We just have to work out the answers to the sums and then the door will open!’

‘Maths?’ George groaned. ‘I hate maths.’

‘I’m good at maths!’ William and Leah shouted at the same time. They looked at each other in surprise and then quickly away.

‘Do we just shout our guesses out loud?’ Mimi said sceptically, eyeing the sand that was now deep enough to cover their feet.

‘Let’s try!’ Leah said urgently. ‘What’s the first sum?’

Khalid stared at the first line, his fingers tracing the markings. ‘Oh, this one’s easy,’ he said confidently. ‘It’s seven plus three. So, the answer is ten!’ He said the last bit loudly and clearly. Leah braced herself expectantly but . . .

Nothing happened.

‘Something about this doesn’t feel right,’ George muttered.

‘What about the other hieroglyph bricks? Like the one I pushed,’ William suggested, wading back towards the large wall covered in gold markings. ‘That one was like a button, so the others probably are, too. You said there were numbers up here, right? Maybe we can use them as a keyboard, to type in our answer?’

‘Genius!’ Khalid cried. ‘The symbol for the number ten looks like a little arch. Can you see anything like that?’

William’s eyes scanned the symbols frantically. ‘Got it!’ he shouted triumphantly, and then he stabbed at the stone.

There was a groaning sound as if the room were shifting. Leah looked towards the door, hardly daring to hope that it would fly open with their first answer. But it remained firmly closed. Instead, more plumes of sand began to shoot out of the walls.

‘I don’t think that’s the right answer,’ Leah said, her eyes wide. Her breathing hitched as the room began to fill with sand even faster. It was up to her knees now. ‘And I think every time we get it wrong, more sand will come pouring in! We’ve got to crack this!’

‘But . . . seven plus three is ten!’ Khalid protested, his eyes bulging.

‘We must be missing something!’ Mimi said, frustrated.

‘Try pressing it again, William,’ Khalid urged.

‘No!’ cried Leah, but it was too late. William had already pressed the brick and now more sand was tumbling into the room with every second that passed.

‘Come on!’ William shouted in frustration, pounding his fist against the wall. He was starting to breathe heavily.

‘We need to stop and calm down! Panicking isn’t going to get us anywhere,’ Mimi cried. The sand had reached her waist, but with some effort, she waded over to Khalid. ‘What else can we try?’

‘Did you say there were letters up there, too?’ George asked, staring at the hieroglyph wall. ‘Maybe we need to spell the word “ten” instead of pressing the number?’

Leah felt a spark of hope, but Khalid was already shaking his head. ‘No, that won’t work. The language we speak in Egypt today isn’t the same as it was back then. I don’t know the Ancient Egyptian word for ten. I only know the symbol. If we have to spell the answer, then . . .’ He trailed off, biting his lip. Leah heard the words he didn’t say. If they had to spell the answers out, they were doomed. They would never get out of this room.

‘It is weird there are numbers and letters up here,’ William said. He was staring up at the wall, his forehead creased in concentration.

‘William,’ Mimi snapped. ‘This isn’t the time—’

‘I’ve got it!’ William suddenly cried. ‘It’s a code!’

‘What?’ Leah frowned. They didn’t have time for this. The sand was coming in too fast.

‘Look at how the letters and the numbers are set out. Each letter has a number underneath it. It’s not the number we have to press – it’s the matching letter! And the letter above the number ten is . . . this one!’ Before the others could stop him, William reached out and pushed a brick with a snake carved into it.

Leah tensed as she waited for more sand to pour into the room, but nothing happened. Instead, there was a heavy clunk. Fighting against the sand that had almost reached her chest, she spun towards the exit, and watched as one of the metal rods holding the door in place suddenly drew backwards.

‘William!’ she cried in relief. ‘You’re right! It’s working! Quick, Khalid – what’s the next sum?’

‘Twenty minus seven,’ Khalid called from the doorway.

‘Thirteen!’ Leah shouted, but William was already moving. The rising sand made it difficult, but he managed to reach up and push the brick with the falcon on it. Behind her, Leah heard the satisfying sound of another bolt thunking back across the door.

‘Leah!’ Mimi suddenly yelled in panic. Leah looked across at her friend. Mimi was the shortest out of all of them, and the sand was up to her chin. She tipped her head backwards, trying to keep her nose and mouth free, panting frantically . . .

‘Quick, Khalid, the last sum!’ Leah cried desperately. If they didn’t hurry up, the sand was going to swallow them whole and suffocate them!

Khalid had extracted Bast from his satchel and now the small cat was perched on his shoulder, eyeing the rising sand nervously. ‘Er,’ Khalid’s eyes scanned the symbols urgently. ‘This one is longer. It’s . . . twenty plus ten, minus twelve!’

Leah’s mind raced as it juggled the numbers. Twenty plus ten was thirty and then take away the twelve was . . . ‘It’s eighteen!’

‘The arch with eight lines, William!’ Khalid called across the room. The sand had reached his chin now.

As fast as he could, William fought his way towards the symbol for the number eighteen and then stretched up to press the matching letter – a strange oval shape with pointed ends. Leah’s eyes flicked to the door, praying the third bolt would move. They didn’t have much time before they would be buried alive!

For a moment there was only a horrible silence, and then the room gave a groan that was different from the earlier ones. Without warning, the third and final bolt scraped back across the stone and the exit sprang open, sand rushing out in a tidal wave. The children went with it, tumbling through the door and out into the empty corridor beyond.