Kate bought a ticket and walked up the stairs to the platform on the floor above, which was shielded from the elements by a grand semicircular metal and glass roof. The station was crowded for this time of day, a large group of French schoolchildren moving slowly along it. Kate walked on beyond them to where a young man was circling on a battered scooter.

A train pulled in and she got on to it. The students boarded with her and she listened idly to the meaningless chatter of someone else’s children. The train pulled out. Grey buildings slid by beyond a rain-splattered window. The burner phone buzzed in her pocket. She answered it. ‘Get off at the next stop. Don’t end the call.’

The train rattled slowly into the station at Hackescher Markt. As the doors slid open, Kate did as she had been instructed. The voice at the other end of the line was silent. She waited. ‘Get back on. End the call.’

She did, just as the doors closed. The train pulled out. ‘I don’t know if I like this,’ she whispered into her lapel.

‘Let’s stay with it.’ It was Suzy, who must have been assigned to the makeshift control room. ‘We’re sticking with you, not far behind.’

‘Easy for you to say,’ Kate muttered. The train rolled on, past Museum Island and across the canal. The phone rang. ‘Get off at Friedrichstrasse. There is a coffee shop on the platform called Cuccis. Buy a coffee and wait.’

Kate was on the cusp of telling the voice at the other end of the line where he could stick his meeting, but he ended the call before she had the chance.

In the coffee shop, she ordered a black coffee and stood drinking it as the platform emptied, then slowly filled again.

The minute hand on the station clock crawled around the dial. Five minutes became ten, then turned into fifteen and finally twenty. ‘I’m crying off,’ Kate said.

‘It’s your call, boss,’ Suzy said, to which Kate very nearly replied, Of course it’s my bloody call. But with the same uncanny sense of timing, the phone rang again. ‘Go down the stairs, cross Friedrichstrasse and head east.’

‘Is this leading anywhere? I’m close to calling it off.’

‘You were followed.’

The call was ended. Kate gritted her teeth. She did as she’d been told, emerging again into the spitting rain on the cobbled street the far side of Friedrichstrasse. She followed its passage east, past a series of down-at-heel cafés and restaurants.

She stopped to drop money into a busker’s hat. ‘Talk to me, Danny,’ she said. ‘He says I’ve been followed.’

‘We don’t know what he’s on about, Kate. We think you’re still clean.’