Carlos kept watch on the orphanage while they brainstormed their plans. Luckily, he’d thought to bring his special reading glasses – which were actually thermal binoculars – and used them to work out a rough map of the building.

‘I think the children are on the fourth floor,’ he said, raising the glasses to the top of his head. ‘There’s more concentrated heat there than anywhere else.’

‘What about the basement or the attic?’ Max asked. ‘They’re the most obvious places to hold someone captive. I doubt they’d keep Nico with the other kids – he’d be more likely to escape that way.’

Carlos put on his glasses again and had a look, but there didn’t seem to be anything bigger than a mouse on either of those levels.

‘How are we going to get in?’ Autumn asked.

Carlos had already worked that out. He’d spotted an old coal chute up against the building that would give them direct access to the cellar. It was shielded from the piazza by a roadworks sign, but there was a padlock.

‘We can’t all go,’ he said. ‘If something happens, we’ll need at least two of us to launch a rescue mission – and perhaps it should be me and Autumn. We’ve had a bit of experience in that department.’

Max grinned, recalling how Carlos and Autumn had come to his and Kensy’s aid in London, when a couple of brutes had tried to kidnap them off the street.

While the children were busy planning, Misha had gone to tell Miss Ziegler what was going on, but the woman wasn’t in her room. Misha then tried the other teachers, but none of them were about either. The only rational explanation was that they were all working on something for the main mission and were meeting somewhere in secret. At this point, it looked as though they were going it alone. She thought about involving the other kids but decided to keep things low-key, at least until they worked out if Nico was actually in the orphanage. Too many trainee agents on a real mission could easily get out of hand.

‘If we’re not back in an hour, you know what to do,’ Max said. Carlos threw him his black beanie and Kensy pulled a sweater over her head.

‘Should we test comms again?’ Kensy asked. She’d given Autumn her watch so that they could communicate through Max’s.

The last time Mrs Vanden Boom had examined it, she’d found a radio transmitter and a tiny earpiece that you could pull out from the dial. In fact, the woman had studied the watches on several occasions now and each time had discovered another fascinating feature.

Autumn gave Kensy a hug. ‘Good luck.’

Max leaned in for one too, which set Autumn’s heart rate on double time. Carlos and Misha gave them a wave as they left the room. The trio watched from the window as the pair headed into the piazza, which was still crowded with tourists.

‘There they are,’ Autumn said, spotting Kensy and Max below.

Max pretended to run his hand through his hair, positioning his watch by his mouth. ‘Can you hear me?’ he asked.

‘Loud and clear,’ Autumn replied, her eyes tracing Kensy’s movements as the girl rounded the back of the roadworks sign. She saw Kensy take out her hairclip and, no more than ten seconds later, she and Max disappeared.

Kensy slid down the narrow chute and flicked on her tiny torch to illuminate the dingy space. Apart from a few lumps of coal in the corner, the room was stacked with pallets of beer and cigarettes. There was another tower of boxes containing olive oil and several sacks of onions, some of which must have already turned bad, given the stench.

Max put on Carlos’s heat-seeking glasses as Kensy listened at the door. Once he gave her the signal, she pulled it open and checked the hallway with a small pocket mirror. ‘It’s clear,’ she whispered, and ventured outside.

The air was thick with damp as the twins crept to the end of the hallway. Max pointed up a set of timber stairs and Kensy stepped onto the bottom tread, wincing as it groaned under her weight. The second step creaked too. Max followed behind her, holding his breath until they reached a small landing. The pair of them crept to a door with a circular glass panel in the top half and froze when they heard voices on the other side. Max had made the rookie error of not using Carlos’s glasses to check if anyone was there.

After a moment’s pause, Kensy stood on her tiptoes and peered through the porthole into a large kitchen. There was an ancient cooker and a long table littered with beer bottles and abandoned dinner plates. Seated around it were the three men who had chased them and the older fellow who they’d seen collecting the stolen items from the children. There was another man in a pinstriped suit with his back to them.

A woman entered the room from a side door. It was Sister Maria Regina. Although dressed in her habit, she was without her wimple. Her long dark hair floated about her shoulders, but it was what she did next that made Kensy gasp in horror. The woman gripped one side of her face, gouging her skin. With a sharp tug, her entire visage came away. Her face was instantly transformed from the middle-aged nun with the huge nose into the young woman who Kensy had seen leaving the orphanage the other night. She then removed her teeth too and put them in a jar by the sink.

Kensy gagged and looked away. ‘Eww. Now, that’s where I draw the line.’

‘What’s the matter?’ Max said impatiently. He didn’t think it was a good idea for both of them to be peering through the window – they were more likely to be seen.

‘It’s the woman,’ Kensy whispered. She turned back in time to see Sister Maria Regina tousle her hair and spotted a mark – no, a word – behind her ear. Nero.

‘Sister Maria Regina is Diavolo too,’ Kensy said out of the corner of her mouth. ‘She’s been wearing a mask this entire time – and it’s gross. Be grateful you didn’t have to see it for yourself. Talk about taking one for the team.’ The girl’s mind suddenly turned to Shugs. Was that how he’d fooled everyone – with a mask? But there was no time to worry about him now. She’d have to mull over that one later.

Unable to resist, Max popped up beside her to steal a peek. He immediately recognised Sister Maria Regina as the woman in the restaurant.

The twins surveyed the rest of the group and noticed that they all had the same word inked onto their wrists. The man in the suit stood up and walked to the other end of the room. Kensy felt a stab of disappointment when she realised he was the fellow who she’d thought had his wallet stolen near the Spanish Steps. Her hunch that he and the boy had been up to something had been right. For now she and Max weren’t going any further – not in this direction, anyway.

‘Ho vinto!’ The older man slapped his hand of cards onto the table and laughed uproariously. He rose to his feet, scraping his chair against the floorboards, then spooned indeterminate food onto a plate and made his way straight towards the twins. They ducked their heads and scrambled back down the stairs, along the passage and into the storeroom. Seconds later, heavy footsteps thumped in the hallway.

‘Nico must be down here somewhere,’ Max whispered. ‘He’s bringing food.’

‘Or they’ve run out of beer.’ Kensy gulped, realising they were definitely hiding in the wrong room if that were the case.

The pair listened at the door then pulled it open ever so slightly. They could see the older fellow pause at the room diagonally across from them. He banged on the door and yelled something in Italian. When there was no reply, he opened a small box in the wall and was about to place the plate of food in it when he must have caught sight of something. The plate smashed onto the floor as he turned the key in the lock. He charged into the room and caused an almighty ruckus before racing out and up the stairs, shouting at the top of his lungs.

The twins closed the door and turned to one another. Kensy’s heart was pounding a million miles a minute. Although her Italian wasn’t the best, she thought she had a fair idea of what the man had said . . . but how was it possible?

Max, his face ashen, raised his watch to his lips. ‘We’re too late. He’s gone.’