‘Clearly your curiosity knows no bounds, Herr Gunther. But I’m sorry to disappoint you. I welcome your assistance, but I see no reason why I should answer all your questions.’

I shrugged. ‘I don’t suppose it matters much now,’ I said.

The Grosse Zug was an inn on one of the two islands between the marshes of Köpenick and Schmöckwitz. Less than a couple of hundred metres in length, and no more than fifty wide, the island was tightly packed with tall pine trees. Close to the water’s edge there were more signs saying ‘Private’ and ‘Keep Out’ than on a fan-dancer’s dressing-room door.

‘What is this place?’

‘This is the summer headquarters of the German Strength ring. They use it for their more secret meetings. You can see why, of course. It’s so out of the way.’ He started to drive the boat round the island, looking for somewhere to moor. On the opposite side we found a small jetty, to which were tied several boats. Up a short grassy slope was a cluster of neatly painted boathouses, and beyond it the Grosse Zug Inn itself. I collected up a length of rope and jumped off the slipper on to the jetty. Six cut the engine.

‘We’d best be careful how we approach the place,’ he said, joining me on the jetty, and tying up the front of the boat. ‘Some of these fellows are inclined to shoot first and ask questions later.’

‘I know just how they feel,’ I said.

We walked off the jetty and up the slope towards the boathouses. Excepting the other boats, there was nothing to indicate that there was anyone else on the islet. But closer to the boathouses, two armed men emerged from behind an upturned boat. Their faces wore expressions that were cool enough to cope with me telling them that I was carrying bubonic plague. It’s the sort of confidence that only a sawn-off can give you.

‘That’s far enough,’ said the taller of the two. ‘This is private property. Who are you and what are doing here?’ He didn’t lift the gun from his forearm where it was cradled like a sleeping baby, but then he did not have to lift it very far to get off a shot. Six made the explanations.

‘It’s desperately important that I see Red.’ He thumped his fist into the palm of his hand as he spoke. It made him seem rather melodramatic, I thought. ‘My name is Hermann Six. I can assure you gentlemen he’ll want to see me. But please hurry.’

They stood there shuffling uncertainly. ‘The boss always tells us if he’s expecting anyone. And he didn’t say anything about you two.’

‘Despite that, you can depend on it that there’ll be hell to pay if he finds out you turned us away.’