‘No,’ said Hanne. ‘We want to find out what we can about the Kestrel escape line. Going in like that could mean everything ending in chaos. Let’s wait and see what happens. They may have other visitors after all.’

Sorensen decided that they’d watch the house overnight and into the following day, and if nothing had happened by the late afternoon – by which time the one-armed man would have been inside for twenty-four hours – they’d move in.

They didn’t need to wait that long.

It had been dark for an hour when a side door opened and two figures moved furtively along a path from the house towards the quiet road in front of it.

The instructions had been that in the event of this happening, they should be allowed to move clear of the house before being challenged. Somehow word hadn’t got through to everyone, because no sooner had the two figures emerged than there was a shout, an order in German to halt, then another shout, followed by a volley of pistol shots. Prince heard Sorensen bellow orders over the radio to move in and stop them. ‘We need to keep the perimeter secure!’ But it was too late: the two figures had ducked back into the house, and were now firing from a ground-floor window. It was then that Prince heard the crack and whistle of a shot, and Hanne screaming behind him, followed by the searing pain in his shoulder.

He was aware of feeling light-headed and nauseous, and felt Hanne’s arm round him as she told him to sit down. Across the road, the Americans were still trying to force their way into the house. Suddenly Hanne shouted out and pointed to what appeared to be the same two figures emerging from the shell of a house two doors along.

But in the chaos, no one heard her, and they could only watch as the two figures hurried to the roadside, reaching it just as a jeep pulled up, the men jumping in as it sped away. By the time, the Americans realised what was going on, it was too late. A couple of them opened fire at the jeep, but its taillights were already dimmer than the stars above them.

Dusk was descending on Cologne as the train from Frankfurt finally pulled into Köln Hauptbahnhof. It had been a long journey, delayed because of speed restrictions, or damage to the track, or for no apparent reason at all.

Two of Walt’s team had followed Charles Falmer onto the train. Prince had made it clear that they should leave him for as long as possible: they needed to see where he went and what he did. The train was crowded, and Walt’s men watched as Falmer found a place in an eight-seater compartment towards the front. They split up, one of them positioning himself at the front of the carriage, the other at the rear.

The train emptied slowly in Cologne, the two Americans waiting for the Englishman to leave so they could follow him. But soon the trickle of passengers dried up, and Charles Falmer had certainly not been among them.