‘No, you really can’t,’ said Dr Smeaton. ‘People think of art and they think of pretty paintings that look nice hanging on the wall. But the people who own art are often the type of people concerned with the easiest way to smuggle large amounts of cash-equivalent goods over a border so they can buy arms or drugs or goodness knows what. Those people are very unpleasant when they’re angry.’

  ‘There’s no-one like that in this case,’ said Friday. ‘It’s a cold case. A crime that took place over a hundred years ago. There’s no-one left alive to be angry with you.’

  Dr Smeaton shook his head. ‘But will I be left alive?’

  ‘Yes,’ said Friday. ‘No-one here is a threat to you.’

  Dr Smeaton came closer and lowered his voice. ‘What about that woman agent?’

  ‘Agent Okeke?’ asked Friday.

  Dr Smeaton nodded.

  ‘You know,’ said Friday. ‘If you just learn her name and job title, that will go a long way to ending any hostility on her side.’

  ‘I used to irritate my ex-wife too,’ said Dr Smeaton.

  ‘A lot of men irritate their wives,’ said Friday. ‘It’s the same deal. The things you dismiss as inconsequential like job titles, anniversaries, picking up socks, they don’t see the same way.’

  ‘Goodness,’ said Dr Smeaton mopping his brow. ‘Inorganic chemistry is so much simpler.’

  ‘I know,’ sympathised Friday. ‘So, are you all ready to analyse the inorganic chemistry of the Mona Lisa?’

  ‘Well, the equipment is all set up,’ said Dr Smeaton. ‘Inspector Barnes has asked me to test a sample from the letter as a case study to make sure it’s all working.’ He pointed to his microscope, where an old piece of writing paper was laid out for examination.

  ‘That’s a good idea,’ said Friday. ‘What results did you get on the letter?’

  ‘It’s one hundred per cent authentic,’ said Dr Smeaton. ‘The paper stock is early twentieth century and the ink is a type commonly used in Italy in the pre-World War One era. I sent a scan to a handwriting expert at Cambridge. She has confirmed it matches with other samples of Peruggia’s writing.’

  ‘That’s a shame,’ said Friday. ‘It would all be so much easier if the letter was a fake and we could dismiss the whole thing as a fairy tale.’

  ‘You’d better give the letter back to Inspector Barnes for his files,’ said Dr Smeaton, taking the letter out from under his microscope, putting it in an evidence bag and handing it to Friday. She glanced at the slip of paper that had triggered their whole investigation and, as soon as she did, she froze.

  ‘What is it?’ asked Dr Smeaton.

  ‘This letter,’ said Friday. ‘It’s a fake!’

  Friday rushed out into the corridor to show Uncle Bernie and Agent Okeke.

  ‘It’s a fake!’ she exclaimed.

  ‘No, that can’t be right,’ said Dr Smeaton, following her anxiously. ‘I guarantee – the paper, the ink, the handwriting – it’s all authentic.’

  ‘Yes, but the content isn’t,’ said Friday. ‘A forger can get hold of a one-hundred-year-old sheet of paper and turn-of-the-century Italian ink. They can spend months learning to copy someone’s handwriting. This letter could be one hundred per cent authentic chemically and stylistically and yet still be a forgery.’

  ‘Well, yes, I suppose. Yes, that’s true,’ conceded Dr Smeaton. ‘Forgers are ingenious. They do go to these lengths, but usually that’s to forge a work of art, not to forge a letter about a work of art.’

  ‘I know this is definitely a forgery from what it says,’ said Friday. ‘Look . . .’ She held the letter up for Bernie to see.

  ‘What am I looking at?’ he asked.

  Friday pointed out one line. ‘This bit.’

  The guards were too busy chatting up a pretty girl to pay any attention to me.

  ‘Well, the French are very romantic,’ said Ian. ‘That’s not so shocking.’

  ‘Not the sentence, the word – chatting,’ said Friday. ‘From the verb to chat.’

  ‘Still not getting it,’ said Uncle Bernie.

  ‘“Chat” did not exist as a verb until after World War One,’ said Friday. ‘Before then, a chat was just a word for a louse – an insect you get on your clothes and skin if you’re dirty for prolonged periods of time. During World War One, the soldiers in the trenches were infested with lice. When they stood around talking to each other they would pick chats off each other. So they started to call those conversations “chats”. So the words “to chat”, “chatroom”, “to chat up” – none of that was in use in 1911.’

  ‘That can’t be right,’ said Uncle Bernie.

  ‘It’s an established historical fact,’ said Friday. ‘Lots of words we commonly use now did not exist before World War One.’

  ‘So this letter is a forgery?’ said Uncle Bernie.

  ‘Yes,’ said Friday. ‘A brilliant, carefully constructed forgery.’

  ‘Then this whole thing about the Mona Lisa being fake,’ said Uncle Bernie. ‘It’s just a hoax?’

  ‘This is a lot of trouble to go to, to start a rumour,’ said Agent Okeke. ‘Why would anyone do that?’

  ‘I’ve got to talk to the minister,’ said Bernie. ‘All the arrangements have been made to bring the Mona Lisa over here for testing tomorrow. We need to call that off.’

  ‘Thank goodness,’ said Dr Smeaton. He slumped down on one of the chairs in the corridor and pressed his hand over his heart. ‘The thought of being responsible for testing the Mona Lisa was giving me chest pains.’

  Uncle Bernie took out his phone and started dialling.

  ‘His phone will be turned off,’ said Agent Okeke.

  ‘What?’ asked Uncle Bernie.

  ‘The minister is at the opera. It’s the premiere of a new production of Carmen tonight,’ said Agent Okeke. ‘It’s France’s greatest opera. As minister for the arts, he will be expected to be there and if he’s at the opera he will have his phone turned off.’

  ‘At least we know where he is,’ said Uncle Bernie, putting his phone back in his pocket. ‘Let’s get over there quickly. We’ll try to catch him in the intermission.’

  Luckily, Agent Okeke drove like a lunatic, so they were across the river and screeching to a halt outside the Paris Opera in less than eight minutes. Agent Okeke clearly enjoyed yelling at the armed police running to intercept them while waving her Interpol ID in their faces.

  ‘This is official government business,’ she yelled. ‘Protect our car while we go inside.’ It was such a strange demand that the gendarmes did not protest as she strode past them and in through the main entrance, Bernie, Friday and Ian following in her wake. Once inside, things became very anticlimactic.

  The ushers were not as easy to intimidate as the police officers. They were used to having extremely rich and extremely pompous people try to bully their way into the performance during the most beautiful of arias. The ushers knew how to say ‘no’ to difficult people, so no amount of angry threats or ID waving from Agent Okeke could get them inside. They would have to sit and wait for intermission to talk to the minister.

  ‘We could pull the fire alarm,’ suggested Agent Okeke in a low voice so the ushers wouldn’t overhear her. They had all been sitting on a large flat couch for a total of three minutes and her patience had run out two minutes and fifty-five seconds ago.

  ‘There are literally laws against yelling “fire” in a crowded theatre,’ said Friday. ‘The panic can be as dangerous as the fire.’

  ‘Pfft,’ said Agent Okeke. ‘No-one wants to take any risk any more. If someone is too stupid to be able to evacuate a theatre without being trampled that’s their own lookout.’

  ‘It’s only twenty minutes to the interval,’ said Ian.

  ‘How do you know that?’ asked Friday.

  ‘It’s Carmen,’ said Ian, listening to the muffled sound of singing coming from within the theatre. ‘This is the bit where José returns and Carmen tries to seduce him with dance. Listen . . .’

  Friday listened, but she couldn’t quite hear. ‘I can’t make it out,’ she said.

  Ian leaned in close and whispered the words in French, ‘Je vais danser en votre honneur . . .’

  Friday suddenly appreciated what everyone had always said about French being the most beautiful language in the world. She closed her eyes and hung on the sound of his voice and the feel of his breath tickling her ear. She swayed towards him. Then, as the aria drew to a finish, Ian snapped back to English and the spell was broken.

  ‘There’s still a bit to go. José hears a bugle call, Zuniga arrives,’ explained Ian. ‘They duel, then José has no choice but to run away with Carmen. Curtain close. Everyone in the audience will rush out to get a drink in about . . .’ Ian checked his watch. ‘Fifteen minutes from now.’

  ‘Urgh, so we have to wait,’ moaned Agent Okeke.

  Ian was sitting next to Friday. He took her hand. ‘Look at us. We’re at the Paris Opera on a Saturday night. It’s like a proper date.’

  ‘We’re hurrying to arrange political intervention in a fake forgery investigation,’ said Friday. ‘That’s not very romantic.’

  ‘That isn’t, no,’ agreed Ian. ‘But this is – where we are – here in Paris. We’re in a beautiful historical building listening to a great soprano sing a beautiful aria about her tragic fate. Forget about the investigation for a while. Just enjoy the moment.’

  Friday looked at Ian’s hand in hers. She closed her eyes and listened.

  The sound was muffled, but that only made the opera more haunting. The final strain of the song reverberated across the lobby and the audience burst into applause. The ushers threw open the doors and patrons started rushing out. The ladies needing to go to the toilet were the fastest off the mark, then the men heading for the bar were close behind.

  ‘Keep your eyes peeled, we don’t want to miss him,’ said Bernie.

  The four of them stood up and scanned the flood of people streaming out into the lobby.

  ‘Isn’t that your roommate?’ asked Ian.

  Friday looked across in the direction he was pointing. It was Sophia. She looked glum. It didn’t take Friday long to figure out why. Sophia was with her father and he was on his phone ignoring her. That was, until he spotted Bernie. Being large and brawny, Bernie was hard to miss. Especially when he was dressed in a crumpled grey suit while all the other men were wearing tuxedos.

  ‘What are you doing here?’ demanded the director. ‘Have you come to dissect the throat of the soprano to confirm that she is real?’

  ‘No, it’s none of your concern,’ said Bernie.

  Friday looked at the ground. This was an untruth. She knew she was bad at lying and didn’t want the director to see into her soul and guess the truth.

  ‘You’re a disgrace,’ said the director. ‘I would say you’re a disgrace to your people, but your people at Interpol all seem as disgraceful as you.’

  ‘Are you enjoying the show?’ Ian asked Sophia.

  She blushed. Friday forgot that she had a crush on Ian. ‘I can’t actually see anything,’ said Sophia. ‘The lady in front of me has a crazy piled-up hairstyle. And the guy behind me keeps coughing on the back of my neck.’

  ‘That is Saul Dreyfuss,’ said the director. ‘He is a great patron of the arts.’

  ‘It’s still gross,’ said Sophia.

  ‘There he is,’ said Bernie, spotting the minister on the other side of the crowd. Bernie dived into the throng and started edging his way towards the minister.

  Friday was going to follow him, but Ian took hold of her hand again.

  ‘And you, sir,’ Ian asked the director. ‘Are you enjoying the show?’

  Friday realised Ian was trying to make sure the director didn’t follow Bernie and interrupt his conversation.

  ‘I don’t know who you are,’ said the director. ‘I didn’t come here to converse with children.’

  ‘They’re my friends from the art school,’ said Sophia. ‘Where’s Epstein?’ She looked about for him. Evidently, even though she could see Ian holding Friday’s hand, it did not occur to her that they were a couple.

  ‘We broke up,’ said Ian.

  ‘You did?’ said Sophia, her face suddenly brightening up.

  ‘You did?’ asked Friday. She was also curious to find out where Ian was going with this one.

  ‘Yes,’ said Ian. ‘I was heartbroken. But Epstein wanted to concentrate on his art without the distraction.’

  ‘Oh, I’m so sorry,’ said Sophia unconvincingly. She was not a good actor. ‘You should get out there and see other people, to take your mind off things.’

  ‘Yes,’ agreed Ian. ‘Friday is helping me come to terms with my disappointment.’

  He held up their linked hands and kissed the back of Friday’s.

  ‘Oh,’ said Sophia. You could almost see her brain struggling to process this information. ‘Oh, I get it. A rebound relationship.’ She nodded. This made sense to her.

  ‘No, I’m pretty sure Friday is the one for me,’ said Ian. ‘I find myself strangely attracted to short, cardigan-wearing girls with no social skills.’

  Friday looked up in his eyes. He was laughing at her. Well . . . he was laughing with her at her, so that wasn’t so bad.

  ‘Yes,’ said Friday. ‘And I find I have a hormonal imbalance that affects my ability to regulate my breathing and retain my balance whenever Ian enters the room.’

  ‘It’s a match made in heaven,’ said Ian.

  ‘Or a petri dish,’ said Friday.

  ‘Either way works,’ said Ian. He leaned towards her. Friday’s hormones were doing that thing where she started to have trouble breathing again. Her eyelids drifted down towards Ian’s lips as his face got closer. Suddenly they were jostled. Friday looked round and realised that the minister had just swept past them.

  ‘Come on, we’re going to talk outside!’ said Uncle Bernie.

  The moment was gone.

  Uncle Bernie guided Friday by the elbow as he followed the minister out through the main doors onto the street.

  ‘What’s going on?’ demanded the minister.

  ‘The letter is a fake,’ said Uncle Bernie. ‘It’s a hoax. There is no reason to test the Mona Lisa.’

  ‘What?’ said the minister.

  ‘The letter uncovered in Italy,’ said Uncle Bernie. ‘Someone went to enormous trouble to create a convincing fake. It’s on the right paper and with the right ink, but the words are wrong. They don’t fit with the time period.’

  ‘So?’ said the minister.

  ‘So, there’s no need to test the Mona Lisa,’ said Uncle Bernie. ‘We can call it off.’

  ‘You’re out of your mind!’ exclaimed the minister. ‘We can’t stop it now.’

  ‘But if the letter is a forgery,’ said Friday, ‘there is no reason to suppose that the Mona Lisa is a forgery.’

  ‘Reality doesn’t matter any more,’ said the minister. ‘It’s about perception now. The whole world thinks the Mona Lisa is a fake. Explaining some detail about the etymology of a word in a letter isn’t going change their minds. The only thing that will convince them now is scientific proof. The tests have to go ahead.’

  ‘But there’s no need,’ said Uncle Bernie.

  ‘Of course there’s a need,’ said the minister. ‘The Mona Lisa is one of the greatest tourist attractions in France. It is the jewel in the crown of the Louvre. For the honour of the people of France, we can’t have its authenticity in question. The scurrilous media speculation must be stopped. Reality does not matter. It is about perception and politics now. The tests will go ahead. I forbid you to tell anyone of this. You should leave – none of you are dressed appropriately. You are drawing attention to yourselves.’

  Bernie looked through the glass doors into the lobby of the Opera House. The people inside were watching as they sipped their cocktails. Everyone was so beautifully dressed and just generally really beautiful. Ian could have blended in if he were wearing a suit, but the rest of them – Bernie, Friday and Agent Okeke – did not. To the people on the inside, they were no better than vagrants. Worse, because vagrants in the street didn’t have the presumption to speak to them directly.

  ‘Okay,’ said Uncle Bernie. ‘It’s your decision.’

  ‘You’re making a mistake,’ said Friday.

  ‘I’m a government minister for the nation of France,’ said the minister. ‘I don’t take advice from teenage girls.’

  ‘A teenage girl once led the French army to overthrow the British,’ said Friday. ‘You should be more open-minded.’

  The minister looked Friday up and down, from her green porkpie hat, to her brown cardigan to her worn red canvas shoes. ‘My dear, you are no Joan of Arc,’ said the minister. He turned on his heel and disappeared back inside the building.

  ‘No-one does disdain quite like the French,’ said Ian.

  ‘Let’s get out of here,’ said Bernie.

  ‘What do we do now?’ asked Friday.

  ‘If our mission is complete,’ said Ian, ‘does that mean we can all go home?’

  Uncle Bernie shook his head. ‘The tests are taking place tomorrow,’ he said. ‘We’ll get new orders when the results confirm what we already know. We should continue in place until then.’

  ‘I don’t like it,’ said Friday, not really speaking to anyone. She was staring at the ground and lost in her own thoughts as she ran through the data in her mind. ‘This is a hoax. Someone put a lot of work into it. Why? What were they hoping to achieve?’

  ‘Chaos,’ said Agent Okeke. ‘And their mission has been accomplished, so now we can move on with our lives.’

  ‘Hmm,’ said Friday. She’d stopped listening. Her enormous brain was working flat out, trying to solve the puzzle.

  Ian looked at his watch. ‘We need to get back to the dorm. We’re doing French archaeology in the Middle East tomorrow morning. We need to be well rested for that. Otherwise, it will put us straight to sleep.’

  The following morning, Friday and the rest of her tutor group were led down to the lowest level of the Louvre.

  ‘This afternoon, you’ll swap with the group from the fourth floor and listen to a lecture on archaeology,’ said Kate. ‘But this morning we’re going to study something amazing – a stone sphinx from Egypt. It’s so heavy that the only place it can be displayed is on the basement level. The building would not be able to support the weight.’