‘Where are they?’ Max demanded.

Lawrence MacGregor sat on the chair in front of him in the basement war room at Ponsonby Terrace. The man’s hands and feet were bound with titanium rope – guaranteed to hold a mountain gorilla.

‘We know everything,’ Autumn said. She tossed her long black ponytail over her shoulder and glared at Lawrence.

Frustratingly, the children had been questioning him for some time but Lawrence seemed determined not to say a word.

Magoo had been despatched to the Pharos Clinic, where Max had waited with him until Mrs Potts arrived. As well as being a brilliant receptionist and crack agent, she was also a trained nurse and until Dr Foster was located, Daphne was the best person to look after the man.

He’d wake to the news that his wife was still alive, but her fate in the longer term was something only Cordelia could decide – as long as they could find her.

Shugs had helped Kensy and Curtis bring an unconscious Tippie to the townhouse and carried her to the basement. She was now being guarded by Monty and Elliot in a locked room.

‘Tippie promised,’ Lawrence finally said.

‘Whatever she promised you was a lie. She used you,’ Kensy said. ‘You were a pawn, and what’s worse is that you didn’t even know the truth. Your family is – sorry, was – Pharos. But you were lost to them. I still can’t believe that Tippie never told you. The woman is a monster.’

‘Now tell us where our family is,’ Max demanded.

This interrogation had gone on for long enough.

‘What do I get in exchange?’ the man asked. His head hung from his shoulders and it was clear he was as exhausted as the rest of them.

‘We’ll let you live,’ Max said. He neglected to tell Lawrence that his time would likely be spent in a secure Pharos facility where he’d have years to think about the choices he’d made.

Kensy had already sent a message to Rod. The helicopter was on standby atop the Beacon building, ready to take the children wherever they needed to go. Once Lawrence told them where that was.

‘I might as well be dead if you’re planning to do to me what we’ve done with them,’ Lawrence said.

‘What have you done with them?’ Kensy demanded. She could feel herself losing control and that wasn’t good.

‘You’re so clever. I’m sure you can work it out for yourselves,’ he scoffed.

Kensy balled her fists and stared at her brother.

Curtis tapped Kensy on the shoulder.

‘Remember that conversation we overheard, Kensy? Tippie said that she was going to bring Max and Autumn to Alexandria and that’s where she was planning to kill us all.’

Kensy nodded. Autumn’s eyes goggled. It was the first time she’d heard this.

‘She said something about the fact that at least we’d be close to family,’ Curtis said. ‘So do you think they could have meant . . .?’

Kensy’s jaw dropped. ‘They’re at Alexandria? But where?’

Max looked at his sister, a realisation passing between them.

‘The prison,’ he whispered.

The twins spun around and stared at Lawrence.

‘Knew you two were clever,’ he said, sneering.

Kensy walked over to the man. She bent down so that her nose was almost touching his.

‘Where is it?’ she hissed.

‘That might be a little bit harder to figure out. It’s one of the cleverest things I’ve ever seen, but you’re so smart, I’m going to leave that for you geniuses,’ Lawrence said, a smug smile on his lips.

Kensy raised her hand.

‘No!’ Max shouted. ‘We don’t stoop to his level.’

The girl lowered her arm and turned to her brother. Max’s face suddenly brightened.

How had he not thought of it before now?

‘Kensy,’ he said, motioning for her to follow him.

The pair walked out into the corridor.

‘Grandpère and Grandmère’s truth serum. Is there any left?’ he asked.

Kensy’s eyebrows jumped up. ‘I think so. I’ll be right back.’

The helicopter trip seemed to take forever. As they were leaving London, flying across the open fields to the north, Rod’s voice came through their headsets.

‘We had a message from air traffic control earlier about a chopper setting down just after midday in the carpark at Hatfield House. Two kids were flying it, apparently. You wouldn’t know anything about that, would you?’ he asked.

The children shook their heads. ‘Nope, it wasn’t us,’ Kensy said.

Rod rolled his eyes. ‘Don’t worry – I’ve already sent a truck to pick it up. Mrs Vanden Boom will have it back in the workshop before she realises it’s missing.’

Kensy turned and grinned at the man from her seat beside him. Curtis, Max and Autumn were in the back with Wellie and Mac on their laps. Shugs was beside them. Kensy still wasn’t one hundred per cent sure he was on their side, so they’d decided they couldn’t afford to leave him in London. Tippie and Lawrence were now locked away at Ponsonby Terrace. Mr Frizzle and Mr Reffell had remained behind on guard duties.

Unfortunately, the truth serum hadn’t worked at all. There had only been a few drops left and while Lawrence confirmed that Anna, Ed and the others were at Alexandria, he hadn’t given them anything more.

When they finally reached the grounds, Rod put down in the usual place. ‘You don’t need to wait,’ Max told him. ‘I think we’ll be here for a while.’

The man let them out of the aircraft, then lifted off into the endless blue sky.

‘Come on,’ Max said as he led the way through into the back of the house.

The group assembled in the rear hallway.

‘Shugs, are you sure you don’t know where the prison is? I mean, you’ve worked here forever,’ Kensy said.

The man bit his lip. ‘I swear, I never knew it even existed until you told me,’ the man said.

‘What about Mr O’Leary?’ Max asked.

‘He’s away on ’olidays in Ireland. Been gone for three weeks. He’s not aware of any of what’s gone on and I doubt he knows any more than me,’ the man replied.

Curtis was standing on his own, whispering something to himself.

Autumn tapped her finger against her lip. ‘There are so many hidden places here, but is there anywhere that you’d never think to put a prison?’

‘The family crypt?’ Kensy said.

Max shrugged. ‘That’s a possibility, although the crypt also houses the newspaper archives, remember?’

‘Your grandmother said that the plans are held in a secure vault at the Bank of England,’ Curtis said.

Kensy and Max nodded. ‘She did. We can call them.’

‘And say what? Your grandmother is missing and we think she’s locked in her own prison, which they have the plans for?’ Autumn said. ‘I don’t think they’d just give you access, somehow.’

Outside, the sound of a dog barking redirected everyone’s attention. Wellie and Mac were in the house, so it wasn’t them.

‘Oh heck, that must be Blue, Mim’s new puppy,’ Shugs said. ‘I’d left him in the shed but he must have escaped. I’ll go and check.’

Kensy wasn’t sure they should let him go, but at least she’d slipped a tracker into his pocket so she could keep an eye on him.

‘Maybe there’s something in the library archive,’ Max suggested.

The children headed upstairs to the automaton.

Kensy found the key while Curtis did the honours, pressing the flower that opened the panelling into the secret space.

Max stared at the myriad moving parts, wondering who would have ever come up with such an extraordinary contraption. The way Atlas held up the world just like the fountain out the front – rising higher and higher, revealing the underworld below. His hands looked as if they were spinning the globe above his head.

The boy stared at the serpents at the statue’s feet. He was thinking about something – about the fountain. Hadn’t Autumn told Kensy ages ago that it had a strongroom beneath it, but that none of the junior agents had ever seen it? He’d asked his grandmother once and she’d laughed and said it was just a myth, but was it?

‘That’s it!’ he cried.

Kensy, Autumn and Curtis all leapt into the air.

‘What are you talking about?’ Kensy demanded.

‘The entrance to the prison,’ Max said. ‘It’s under the fountain.’

The Atlas fountain stood in front of the house. The pond around it was divided into four segments bordered by sandstone walls.

‘Do you want to go, or will I?’ Kensy said.

Max jumped onto the edge of one of the small sandstone dividers and balanced like a tightrope walker as he walked to the centre.

Curtis and Autumn looked at him expectantly.

Max reached out to touch the globe. At first he didn’t think it was going to move, but after he pushed harder it began to spin. As it did, Atlas rose higher and higher – holding up the earth above him – while a spiral staircase appeared down below. Max jumped onto it. The others joined him and they all charged down the stairs into the subterranean prison.

‘Hello!’ Max called. ‘Is anyone here?’

The other children joined in, but their voices simply echoed in the long chamber. Then there was nothing.

The corridor must have been fifty metres long. There was no evidence of cells anywhere.

‘Max, look at this!’ A control room not dissimilar to what they’d seen at Moonlight Cove was the only thing that was lit up. The children barged inside. On the wall, there were a series of numbered levers.

Without another thought, Max began to pull on them. Suddenly, lights began to come on down the corridor and, one by one, huge panels started to slide open. Seconds later, faces appeared.

Mrs Vanden Boom was the first to step outside. She was followed by Autumn’s mother in the cell next door. Autumn ran to the woman and soon found her father emerging from the adjacent room.

Kensy raced along the passage, elated to see Song, Sidney, Peter, Mim and Fitz. Dr Foster poked her head out of another cell.

Kensy baulked at the prisoner who was beside her Uncle Rupert.

‘I don’t think so, Dash Chalmers,’ Kensy shouted, and called to her brother to lock down number nine. The man was standing in the doorway. Kensy gave him a shove.

‘Oh, come on, Kensington, you don’t mean that,’ the man cried as the door clanged shut.

Kensy ran to the next room. Her mother hurried out and hugged the girl tightly, quickly joined by her father from the next cell down. Max had run to join her. Then –

‘Granny!’ they yelled as Cordelia appeared. The twins clung to her.

The woman’s jaw dropped as she spotted all of the other prisoners. ‘Oh, my darlings, you saved us,’ she gasped.

Max nodded.

‘And we saved Pharos too,’ Kensy said.

‘I don’t doubt it for a second,’ the woman said. ‘How about we get out of here? I could murder a cup of tea.’