‘I was brought up by a single mum. My dad left when I was five after beating us both so badly we ended up in hospital. She was a cleaner, started her own business … I’ll leave you to work out the rest.’

‘Are you single?’

Kate almost spat her drink out. ‘Jesus Christ, Julie, cut it out.’

‘Very,’ he said, and smiled again. He crossed his endless, perfectly toned legs. But now it was Kate he was grinning at.

‘Enough.’ Kate looked from Callum to Julie and back again. ‘This is not a game,’ she told them both. ‘There’s no reason to suppose we’ll be at risk tonight, but the moment we try to make contact with Natasha Demidova, we’re leaping into the unknown. And we have no back-up. So this is not a joke.’

Callum uncrossed his legs and gave her his full attention. He’d taken his ticking off well, even if it wasn’t really intended for him. ‘I understand that, Mrs Henderson.’

‘There is risk. And if you’ve not absorbed that yet, I’m putting you on notice of it now.’

‘Got it.’

‘Yeah, I’ve been thinking about that,’ Julie said. ‘Is it wise to plunge into this alone? Couldn’t we have asked for backup from Five, or even the military, just not told them the reason?’

Kate’s eyes flashed. ‘No. We’re on our own. All the way through. So if either of you have a problem with that, now’s the moment to abandon ship.’

‘Sounds like an adventure, Mrs Henderson.’ Callum recrossed his legs and tapped the side of his left trainer with his right hand. ‘That’s why I’m here.’

Callum had arranged to meet the diplomat Tess Winkelman at 1924. The restaurant had been founded by White Russians fleeing the revolution and recently been refurbished to bring a hint of modernity to the St Petersburg of the Tsars. ‘Tess chose it,’ Callum explained to forestall any questions, though a quick survey of the menu suggested it was a much less extravagant decision than the hotel. ‘Apparently Garbo came here,’ he went on. ‘And Mata Hari. And Agatha Christie.’

‘Together?’ Julie asked.

‘Yeah.’

‘Really?’

‘Of course not.’

She kicked him under the table.

Kate was about to reprimand her, but thought better of it. She’d played Julie’s mother, older sister or schoolmistress too many times.

The restaurant’s pristine chequerboard floor, tall gilt mirrors, white tablecloths and dozens of images from old Russia and Istanbul glittered in the light cast by the chandeliers. A bar was tucked beneath a wooden orchestral balcony at the far end of the room.

‘From Russia with Love,’ Kate said, interrupting a waiter’s stately progress to demand their version of a Dirty Martini. Maybe a little too quickly: she was becoming aware that the days when she drank now vastly outnumbered those when she didn’t.

Julie said she’d have the same and Callum ordered another beer. ‘You want to watch her,’ Julie said. ‘She’s a very, very bad influence.’

‘How long have you worked together?’ Callum asked.