Kensy and Max barrelled towards a uniformed officer who was stationed outside the police tape surrounding the side entrance of the Tate Gallery.

‘Please can you help us?’ the boy puffed.

The officer eyed them warily. ‘What’s happened?’

‘We were just kidnapped by a man driving a black cab. The whole back was a capsule and we could see out but no one could see in,’ the boy said, struggling to catch his breath. ‘We were stopped at a checkpoint around the corner and we managed to escape through the boot.’

The young constable chuckled. ‘Okay, James Bond, I think you and your girlfriend had better be getting to school. We don’t have time for pranks. Someone disabled the security system and the Graff Peacock’s been stolen. It’s worth a fortune and no one saw them go in or out. Sounds like a tunnel job, if you ask me. But then you two could probably solve the crime, couldn’t you – given what you’ve imagined just happened?’

‘Oh for goodness sakes,’ Max shouted. ‘Why is everyone in London out to get us?’

Kensy looked at her brother, her mouth opening and closing like a goldfish. Was this really her cool-headed twin talking?

The police officer rolled his eyes. ‘Good one, kid. You should be an actor, you know.’

Max took a few deep breaths then turned to his sister. ‘Sorry, I don’t know what got into me.’

With sinking hearts, the children realised they were getting absolutely nowhere with this fellow and decided the only thing to do was to go home and tell Song. He’d believe them. The twins took off, thinking it was probably safest to take the main road, although the mere sight of a black cab almost sent Kensy skywards.

‘Who do you think that guy was and what did he want with us?’ Max said, as they dashed past another police cordon. Traffic was building up as drivers were questioned and redirected.

Kensy shook her head. ‘It must have something to do with Mum and Dad. All of this weirdness began with their disappearance.’

The kids charged past The Morpeth Arms, which hadn’t yet opened, and were nearing Ponsonby Terrace when Claudia appeared around the corner. Max almost ran straight into the pram she was pushing and only just managed to stop himself in time.

‘My gosh, you two,’ Claudia said, looking concerned. ‘What’s happened? Shouldn’t you be at school?’

‘We were kidnapped by a taxi driver, but the stupid policeman didn’t believe us,’ Kensy blurted. ‘We’ve got to find Song.’

Claudia’s eyes widened in disbelief. ‘What do you mean you were kidnapped?’

Max quickly filled her in on the details. Unlike the young constable, though, the woman hung on to his every word.

‘And the Peacock Brooch has been stolen from the Tate,’ Max added. ‘We only saw it yesterday.’

Kensy’s mind was racing. She was thinking about Mrs Brightside and those gadgets she and Max had returned to her last night. She looked at Max and Max looked at her.

‘Mrs Brightside!’ the children gasped in unison.

‘She hasn’t been renovating,’ Kensy said slowly.

Max nodded. ‘She’s been tunnelling.’

‘What?’ Claudia’s brows appeared ready to leap off her forehead.

‘It was Mrs Brightside and the other lady who works at the gallery and Derek Grigsby,’ Max said. ‘They took the Peacock Brooch.’

Talking at the speed of light, Kensy relayed their visit to the Tate and the contents of the envelope addressed to Esme Brightside. ‘I knew that old lady was full of secrets! Those gadgets in the envelope were probably for the alarms and cameras,’ the girl said, ‘and it was that other woman who works there who gave them to her. No wonder she was so happy I’d returned them.’

‘And Derek hasn’t been renovating – he’s been digging!’ Max exclaimed. ‘I’d put money on him having found a tunnel from the old prison that goes straight to the gallery. That’s how they’ve done it. This whole area is riddled with them. Gary at the pub told us.’

‘Esme Brightside might be ancient but she’s tricky,’ Kensy told Claudia, who was looking more incredulous by the second. ‘I saw her through the curtains one night doing flips and jumps. I bet it was her who got the jewel. And, Max, remember how Derek said she was an Olympic gymnast when she was young?’

Claudia put her wrist to her mouth and spoke so quickly the children didn’t catch what she said or what exactly she was doing. ‘They’ve probably already left the country, but notify the airports anyway,’ the woman finished.

Max recalled the brochures splayed across Esme Brightside’s coffee table. ‘They’re heading for the Dominican Republic, to be precise.’

Kensy nodded. ‘And their husbands are meeting them at LAX. That’s the international airport in Los Angeles.’

Claudia’s face drained of colour. The poor woman looked as if she was about to faint. ‘I’ve been on this case for over a year and two eleven-year-olds have solved it,’ she wheezed. ‘I’ll be sacked for sure.’

It was the children’s turn to look surprised.

‘Who do you work for?’ Max asked.

Claudia pointed across the river.

‘You’re MI6?’ he said, his eyes wide. Max gestured to the pram. ‘There’s no baby, is there?’

Claudia shook her head and lifted the covering on the pram to reveal a doll and a transmitter that made baby noises.

‘So that’s why you weren’t keen for me to have a look,’ Max said, a grin creeping on to his face. ‘That’s really cool.’

‘Not if I let them get away.’ The woman’s shoulders slumped. ‘It’s bad enough we lost Garnet Brightside, Walter Grigsby and Ray Daggett a year and a half ago. The three old geezers pulled off the greatest diamond heist in history before skipping town, and I’ve been watching their wives for a year, hoping they would lead us to them. And now you’ve gone ahead and cracked the case.’

‘Come on, let’s go,’ Kensy urged. ‘They might still be around.’

Claudia didn’t need to be told twice. She took off up the road, abandoning the pram on the footpath. Max hesitated, thinking an unattended pram would attract far too much attention. He grabbed the handle and the three of them tore around the corner with Claudia speaking into her sleeve the whole way. They pulled up sharply at the sight of Derek standing beside his blinged-up hatchback with the driver’s door open. His mother was in the back seat with Ivy Daggett, who Claudia identified as the lady who worked at the Tate Gallery.

Claudia and the children approached silently, getting close enough to hear what they were saying.

‘’Urry up, Esme!’ Wanda called. ‘The ship’ll leave without us.’

‘Did she just say a ship?’ Claudia whispered. ‘Didn’t you hear Esme tell her husband that she was meeting him at LAX?’

Kensy nodded.

Claudia whispered into her sleeve. ‘On my signal …’

‘Oh, put a sock in it, Wanda!’ Esme grouched, closing her front door. ‘You’d better not give me the irrits – we’re a long time gettin’ there and a long time gone, if you don’t remember.’

‘I wish I could see the look on Dad’s face when ’e realises we’re not meetin’ ’em.’ Derek grinned his shiny smile. ‘Serves ’em right for leavin’ us and gamblin’ away all the money. That’s a very good idea callin’ the FBI once we’re safely away. That’ll show the old geezers who can really pull off an ’eist.’ And it doesn’t ’urt that I’m a genius that worked out the Dominican Republic ’as no extradition treaty wiv England.’

Esme threw her walking stick onto the ground and practically catapulted herself into the passenger seat.

‘Go!’ Claudia shouted.

The children were stunned to see agents appear from everywhere, surrounding the vehicle with their weapons drawn.

‘Sorry, kids, I’ve got to run,’ Claudia said, and charged off to lead the arrest.

A silver van hurtled into the street followed by a tow truck and, within less than a few minutes, the four thieves were gone and Derek’s blingy hatchback with them.