The journey through the endless pine forests passed swiftly, as she turned over the last conversation in her mind. It was better, perhaps, not to chase one’s tail in a state of doubt and confusion, always seeking yet more agents of the enemy: it had undone so much good work in intelligence agencies all over the world, from the days of the CIA’s James Jesus Angleton onwards. But Julie had had a point when she’d raised the schoolboy friendship between Sir Alan and the prime minister. On some level, it bothered her too.

It was dark by the time she reached the Vaalimaa border crossing, the European and national flags cracking crisply above it in the breeze on the Finnish side as she waited behind a long line of lorries. The wind blew in from the Baltic in great gusts, buffeting the hire car and unsettling her. It was half an hour or more before she was presenting an Irish passport in the name of Kate McGillis to the stony-faced young man in the glass booth on the Russian side of the crossing. ‘Dobrý den,’ she said.

He didn’t look up. He swiped the passport through the computer and glanced over the accompanying paperwork. All her passports – she had six at any given time – had in-date tourist visas for Russia.

The young man, his skin as flawless as his expression was impassive, stared at his screen for what felt like an age. ‘Drive your car in to the right here and step out,’ he instructed her in English. ‘My colleague wishes to speak to you.’

Kate did as she was told, her heart thumping. By the time she had parked, a woman was waiting for her. She was young too, with blonde hair pulled back tightly and bright blue eyes. ‘Please come this way.’

She ushered Kate into a room with a table and two chairs on either side of it. The woman sat, the passport and accompanying entry form in front of her. She might have been pretty, but for the angular set of her chin and skin marked by childhood acne. ‘What is the purpose of your visit to Russia?’

‘I have always wanted to visit St Petersburg. I’ll only be here for a few days.’

‘Where are you staying?’

‘At a hotel on Admiralty Embankment.’ Kate pointed at the form she had actually filled out in the office in London before she’d left. Then she took out the Expedia booking confirmation and pushed it across to her.

‘Do you have friends in St Petersburg?’

‘No.’

‘You travel alone?’

‘Yes.’

‘When did you arrive in Finland?’

‘This lunchtime.’

‘Why did you not fly direct to St Petersburg?’

‘I had a friend in Helsinki I wanted to see. We had lunch together.’

‘Where?’