‘Other than cash,’ said Harper when he met up with Prince and Hanne at the end of the investigation. ‘The accountant chaps – though one’s a woman, believe it or not – say there’s a higher level of cash deposits and withdrawals than one would expect, but then of course one can’t trace cash, so that in itself is suspicious.’

‘So no one paid money in by cheque? I thought that when Anthony Hawke donated money to them, he did so by cheque?’

‘As payment for the purchase of an artwork… these chaps are quite clever. But the evidence of significant amounts of cash going in and out of the account probably means we should persist with this.’

The gallery on Cork Street was watched for a fortnight, and Bourne and Ridgeway were followed, but no clues emerged. Prince said they were especially interested in the woman – the one who’d been at the meeting between Bourne and Hawke and whom he suspected was involved in the Nazi spy ring – but there was no sign of her.

Hanne told him in no uncertain terms that she felt the investigation was ridiculous. ‘Like that sport you play – cricket. It’s slow and pointless. There seems to be no sense of urgency. Surely we should be getting warrants to search the gallery and their homes and bringing them in for questioning.’

Prince said he had to agree, and he arranged a meeting with Tom Gilbey. MI5 are rather dawdling, sir, I think we need to up our game…

But before the meeting could take place, a message came from Berlin, from Bemrose. Gurevich wants to see you. He says it’s urgent – it’s to do with kestrel.

‘We’ve found him!’

Commissar Iosif Gurevich clapped his hands and stood up. There was a wide grin on his face and a shot glass of vodka held high above his head as he prepared to deliver yet another toast. Slightly confused, and beginning to feel the effects of the vodka they’d already been obliged to consume, both Hanne and Prince slowly stood too before sipping their drinks.

It was late in the morning in Gurevich’s new office on the top floor of the building on Behrenstrasse. This one had sweeping views of what remained of Berlin and felt more like a dining room than an office, with its highly polished furniture and expensive-looking rugs. Hanne and Prince were exhausted from their overnight flight from London: they’d hoped for some time in Berlin to rest before their meeting, but Bemrose had insisted they travel to the Soviet zone immediately.

‘You found Friedrich Steiner?’

Gurevich shook his head as he topped up his glass.

‘His father, then?’

‘No, not yet – but hopefully very soon. You recall the file I showed you last time – this one here?’

He angled a folder on his desk so they could see it better. ‘This is Wolfgang Steiner’s file and it gave us a link between him and the Kestrel Line, if you remember. We assumed FFM stood for Frankfurt, which from what you tell me was probably a correct assumption, but we had no idea what the other initials – RLB, V and T – stood for, though we thought T must be Turin. I said at the time that these were notes added to the file after an interrogation, and that the officer who made them had failed to include his initials – that he was most probably in a hurry. I also said I’d try and find that officer.’