When the ferry from the mainland arrived the next morning, we were watching it from the Dulcibella 's cabin.

"Who's that with him?" I asked. It was a short, fat, older man, with glasses and a hard-looking, clever face.

"They haven't got off!" I said. "Where are they going?"

"That's Dollmann," said Davies, "the tall one with the beard."

Five or six passengers got off the ferry, but Dollmann and his companions stayed on the deck. They stared down at the Dulcibella as the ferry moved out of the harbour.

"He must be the engineer from Bremen, who von Brüning told us about. Look, there's Grimm, behind him."

We had to go into Norderney town to buy food and milk, and to collect my post. I was surprised to find that there were two letters for me from my boss. The first one gave me permission to take another week's holiday. The second one, written two days later, and marked "Urgent", cancelled this permission, and told me to return as arranged. I showed them to Davies.

"Juist," Davies answered. "It's the only other stop."

"And from Juist to Memmert," I said softly.

"Memmert!" he said. "That's an idea! It's a long way, of course, twenty kilometres, more or less."

"I haven't received this second one," I said with a smile.

As we made our way back to the harbour, a thick curtain of fog rolled in from the sea. "We'll never find the yacht in this fog," I said, as we climbed down to the dinghy.

"Yes, we will," said Davies. "Just row straight across the harbour." He leaned over the side of the boat, feeling in the water with a stick. "There we are," he said, after a few moments. "That's the edge of the deep water channel. Now all we've got to do is follow it until we reach the Dulcibella. It couldn't be simpler." And, sure enough, in two or three minutes we were back on the yacht.

"Why not go to Memmert?" I said quietly.

"Well," he replied. "If we had a chart and a compass, I suppose we could go anywhere."

"That's extraordinary," I said. "How far could you go like that?"

"Yes," I said eagerly. "But what a chance! Everyone's seen the Dulcibella here, including Dollmann and his friends. If we could get to Memmert in this fog, we might find out what's going on. And no one would see us on the way, or know we were there."

I had got the boat ready by the time he joined me. "We'll have to hurry," he said. "We can't take the open sea route, round Juist. It's too public -- that's the way the ferry goes. And it's more than twenty-five kilometres. No, we'll have to go over the sand. It's a much shorter way, but it'll be difficult because the tide's falling, so the channels through the sandbanks will be extremely narrow and shallow. Are you sure you can row there and back?"

Davies took down the chart and studied it. "Put some food and water in the dinghy," he said. "And an oil lamp, the compass and the guns."

"The guns?" I said. "What for?"

"We're looking for ducks, if the fog clears," he smiled. "Now, just give me ten minutes with the chart."

Even at high tide, the chart only shows narrow channels between Norderney and Memmert, and in a little over three hours" time, it would be low tide. The fog made the sandbanks completely invisible, but Davies did not attempt to look around for buoys or marker posts. Instead, he concentrated all his attention on the chart, the compass, and his watch. My duty was to be a machine, to keep the dinghy moving in whatever direction he wanted. I pulled hard, breathing deeply and regularly, hoping I would be fit enough to manage the journey.

"You steer, and I'll row all right," I said. And we set out.

At the shallowest point, Davies dropped the lead line into the water, and measured the depth. My oar touched sand, and we were aground. I rested for a moment, while Davies looked at his chart. Then we were off again, with a push from the oars on the sandbank, and I could see from Davies's shining eyes that we were in the right channel.

We continued in this way, rowing and pushing, through the soundless white blanket of fog. I began to lose all idea of time and place. The misty figure of Davies in front of me seemed as dream-like and crazy as myself, and I saw strange, imaginary shapes appearing out of nowhere.

It was a race against time, the fog, and the falling tide, but in the early afternoon we arrived at Memmert. In four and a half hours I had rowed twenty kilometres, and Davies had steered us through fog and sandbanks without a single mistake. I let my tired muscles relax, and we had some whisky, bread and cold meat, while making our plans. We decided Davies would stay with the boat, while I explored. I spoke the language well, and in my sea-boots, sailing clothes, and old hat, I could easily pass for a Frisian Islander in the fog.

"Take the compass, the chart, and the whistle," said Davies. "Remember the tide -- you can have an hour and a half, no more. If you can't find your way back, blow your whistle, and I'll blow mine to guide you. Good luck."

The chart showed that the office building was north-west of where we had landed. "That means south-east to come back," I said to myself. I checked the compass, and started up the beach.

I could hear a number of men's voices, so I moved away from the sound, round the corner of the building, and saw a lighted window ahead of me. It would be interesting to see into that room, I thought, so with my hat pulled well down, I walked slowly on, taking a long careful look inside as I passed. It seemed to be an office. I could see Grimm paying a workman some money, and in chairs round the room I could see von Brüning and Dollmann, and the short, older man from the ferry (who was, we learnt later, the Bremen engineer, Böhme). The room was brightly lit and no one was looking out through the window, so I went back for a closer inspection. Bending low, I moved, as quietly as a cat, until I was beneath the window. Then, with great care, I raised my head.

I could only see a few metres ahead of me in the fog, but I could hear noises all around me -- a ship's bell, and some men calling to each other in German. Somewhere in front a door banged. Before long, I found myself on a path, and a few moments later a wall appeared, which seemed to be the side of a building. I paused, and took out my pipe and lit it, to give myself an excuse for standing still and listening.

There was a different workman in the room now, also receiving his wages from Grimm. There were charts on the wall, and the plan of a ship. On the floor were several pieces of old wood, perhaps from the wreck itself. My heart sank. This was pay-day, with the boat crews and divers getting their wages -- just an ordinary meeting of the directors of the company. Davies and I had come all this way for nothing!

Two more men came in to get their wages, and left. Then Grimm stood up and came over to the window. I quickly bent down low, and heard above me the curtains being pulled shut. There was the sound of chairs moving, and people sitting down. Another meeting seemed to be beginning.

Desperate to hear what they were saying, I put my ear as close to the window as possible, but I could only hear a few words now and then. First Dollmann spoke for several minutes. He seemed to be talking about a recent visit to England, and I heard the word "Chatham". Next, Böhme went through a report. He used the letters A to G; seven letters, with figures added to each of them, like this: "A… bad… one point five; B… three weeks… thirty; C… thirty-two… one point two." And so on. Then he asked Grimm about each of these seven letters. I could only hear odd words of Grimm's answers: "tugs", "railway", "pilots", "depth of water", and the name "Esens".

I nearly turned and walked away at that point, but the faint voice of reason told me to be patient. "There are your four men," the voice said. "Wait."

"Very well, sir," Dollmann said, more loudly than before. "I'll invite them to dinner this evening. You can see them then."

We would have to get back to the yacht as quickly as possible. I was just about to move, when I heard movement inside the room. Two of the men pushed back their chairs and stood up, and I heard the door open and close. Who had left, and who remained? I waited, my ear hard against the window.

"Ach!" said von Brüning, sounding astonished.

Suddenly I heard Böhme ask about "the two Englishmen". They were talking about Davies and myself. It seemed that Böhme wanted to meet us.

"He insists on coming," said Böhme.

"I said on the 25th. The tide will be right. He'll come on the night train, of course. Tell Grimm to be ready."

"Only one, with half a load," replied Böhme. "How's the fog?" he added.

I slid away from the window before von Brüning pulled back the curtain. I looked at my watch -- I had been away nearly an hour and a half. I had to get back to the boat, so I checked the compass and started walking. As soon as I was about a hundred metres from the building, I began to run. When I reached the shore, the tide was coming in fast but there was no sign of Davies or the dinghy. I had no time to go looking for them, so I blew my whistle. Almost immediately I heard another whistle some way off, behind me. I turned and ran towards it, blowing my whistle again. The other whistle answered and, a few moments later, I saw the dinghy.

There was a question from von Brüning.

We both rowed and, with the rising tide to help us, we covered the distance in about three hours. Soon after we left, a wind began to blow from the west, and the fog rolled away as quickly as it had come. We were almost at Norderney when we saw behind us the lights of a motorboat. Davies guessed it was the Blitz 's launch, and we watched it draw level and pass us, going in the direction of Norderney.

"Right," said Davies. "The tide's coming in, and the sands will be covered. We can take the direct route back to Norderney over the sandbanks."

"Now they'll know what we've been doing!" I cried.

"Quick, Davies," I called softly. "We must get back. Dollmann's going to invite us to dinner this evening."

"No, it's too dark now for them to recognize us," said Davies. "Let's slow down a bit. We don't want them to see us arrive looking all hot and exhausted. We'll have to pretend we just went out for a row. Will you be able to talk to them? My German's not good enough for that."

"No, but I'll have to make the effort. If they suspect us now, we're finished."

"Give me your oar, old man, and put your jacket on." He lit his pipe, and rowed slowly on, while I lay back, trying to separate my mind from my exhausted body.

When we arrived, the launch was anchored beside the Dulcibella, but we could only see two of von Brüning's men on deck. Then we saw von Brüning himself appear from the Dulcibella 's cabin.

"Is that you, Herr Davies?" he said. "We came to see you!"

Then someone else came up the ladder from the cabin, and Dollmann appeared. Davies sat quietly in the dinghy, looking up at his enemy, while Dollmann stared down at him from the deck of the Dulcibella. It was fortunate that Davies's expression was hidden in the darkness, but the lights from the launch fell pitilessly on Dollmann's smiling face, and showed me the thin lips and cold eyes of the man who had tried to drown my friend.

Meanwhile, the third of our uninvited guests, Herr Böhme, had reached the top of the ladder. There they stood, the three of them, like guilty schoolboys caught stealing apples, while we, the true offenders, only had to listen to their explanations. Dollmann explained he had seen the yacht in the harbour, and had called on his return from Memmert to ask us to dinner at his house. Finding no one on board, he had meant to leave a note for Davies in the cabin. "My friend, Herr Böhme, was eager to see round the yacht, and I knew you would not mind," he added.

"Where have you been?" asked von Brüning, smiling.

"Not at all," said Davies pleasantly. "And we'll come to dinner with pleasure. But we must change clothes first."

"Looking for ducks again," I added, lifting my gun.

And with some embarrassment, the three men stepped on to the launch, which moved smoothly away. We went straight down to the cabin to see what they had been looking at. Everything was just as we had left it, except Dollmann's book, which was pushed right to the back of the shelf.

"Aha!" I said, showing it to Davies. "I think this proves Dollmann has something to hide from them."

"No luck, I suppose?" laughed von Brüning. "Come, my friends, we must leave these young sportsmen to get changed, and talk to them later."

"Oh, rowing about since the fog cleared," said Davies.

"It's quite complicated, wondering who knows what," I said. "Dollmann can't be sure what we know, and must be terrified of the others finding out that we know who he is -- if we do. It's becoming clear, though, that they don't trust him."

"Yes," said Davies. "It shows that they know his real name -- or why would he try to hide the book from them? But they probably don't know he wrote a book, and that I have a copy."

"Islands, of course," replied Davies.

I had told Davies what I had heard and seen on Memmert as we rowed back. Now, as we quickly washed, and changed our clothes, we went over it again.

"What are there seven of in this area?" I asked.

"Yes, but what about 'railway' and 'Esens'?" I said. "And someone insists on coming, on the night train, on the 25th. It must be someone important. Böhme, von Brüning, and Grimm are going to meet him. Somewhere at high tide, probably. And Dollmann probably doesn't know about it as they didn't discuss it until he was out of the room."

"To London!" cried Davies, looking shocked.

"Look," I said, "we want a fresh start. We need to find out a lot more, and we need to prove to them that we're harmless. I suggest that I go back to London."

Davies thought for a moment. "Well, it could be Norddeich. There's a station there, and, let's see… high tide will be somewhere between ten-thirty and eleven o'clock on the 25th. What shall we do?"

"I can find out about Dollmann's past there, and then come back here, as somebody else, to follow up the clues on the 25th. Meanwhile, you must stay here, pretend you want to do a little duck shooting, that sort of thing."

"What are we going to say?" demanded Davies, in a worried voice.

"We haven't got time to think about it now, or we'll be late for dinner. I think they want to inspect us, or at least, Böhme does, and he's obviously the important one."

"I'll be no good alone," he said miserably. "I really don't like the idea, but I trust your judgement."

"Not a word about where we've been today," I said. "If they discover that, we'll be in trouble, and in prison too, probably. For the rest, tell the truth. It's all we can do."