"Any answer, sir?" inquired the boy, when he saw I had finished reading.

"Yes, Charles," I said; "there is an answer, but I'm afraid I can't send it by post. Wait a minute, though," I added, as he began to put on his cap, "I want you to send off a wire for me if you will. It will take a minute or two to write."

I went into the hut, and hastily scribbled a telegram to Latimer, telling him that I had written to McMurtrie, but that otherwise there was nothing to report. I copied this out carefully in the simple cypher we had agreed on, and handed it to the boy, together with five shillings.

"You can keep the change," I said, "and buy fireworks with it. I've been too busy to make any yet."

He gurgled out some expressions of grat.i.tude and took his departure, while I renewed my attack upon the sardines and bread.

Fortified by this simple cheer, I devoted the remainder of the morning to tidying up my shed. I felt that I was living in such uncertain times that it would be just as well to remove all possible traces of the work I had been engaged on, and by midday the place looked almost as tidy as when I had first entered it.

I then treated myself to a cigar and began to keep a look-out for Joyce. She had not said in her letter what time she would arrive, but I knew that there were a couple of trains early in the afternoon, and I remembered that I had told her to come straight to the hut.

It must have been getting on for two when I suddenly caught sight of a motor car with a solitary occupant coming quickly along the Tilbury road. It pulled up as it reached the straggling plantation opposite the hut, and a minute later a girl appeared from between the trees, and started to walk towards me across the marsh.

I was a little surprised, for I didn't know that Joyce included motor driving amongst her other accomplishments, and she had certainly never mentioned to me that there was any chance of her coming down in a car. Then, a moment later, the truth suddenly hit me with paralysing abruptness. It was not Joyce at all; it was Sonia.

I don't know why the discovery should have given me such a shock, for in a way I had been expecting her to turn up any time. Still a shock it undoubtedly did give me, and for a second or so I stood there staring stupidly at her like a man who has suddenly lost the use of his limbs. Then, pulling myself together, I turned away from the window and strode to the door.

She came up to me swiftly and eagerly, moving with that strange lissom grace that always reminded me of some untamed animal. Her hurried walk across the marsh had brought a faint tinge of colour into the usual ivory clearness of her skin, and her dark eyes were alive with excitement.

I held out my hands to welcome her. "I was beginning to think you'd forgotten the address, Sonia," I said.

With that curious little deep laugh of hers she pulled my arms round her, and for several seconds we remained standing in this friendly if a trifle informal att.i.tude. Then, perceiving no reasonable alternative, I bent down and kissed her.

"Ah!" she whispered. "At last! At last!"

Deserted as the marsh was, it seemed rather public for this type of dialogue, so drawing her inside the hut I closed the door.

She looked round at everything with rapid, eager interest. "I have heard all about the powder," she said. "It's quite true, isn't it? You have done what you hoped to do?"

I nodded. "I've blown up about twenty yards of Canvey Island with a few ounces of it," I said. "That seems good enough for a start."

She laughed again with a sort of fierce satisfaction. "You have done something more than that. You have given me just the power I needed to help you." She came up and with a quick impulsive gesture laid her two hands on my arm. "Neil, Neil, my lover! In a few hours from now you can have everything you want in the world. Everything, Neil--money, freedom, love--" She broke off, panting slightly with her own vehemence, and then drawing my face down to hers, kissed me again on the lips.

I suppose I ought to have felt rather ashamed of myself, but I think I was too interested in what she was going to say to worry much about anything else.

"Tell me, Sonia," I said. "What am I to do? Can I trust your father and McMurtrie?"

She let go my arm, and stepping back sat down on the edge of the small table which I had been using as a writing-desk.

"Trust them!" she repeated half scornfully. "Yes, you can trust them if you want to go on being cheated and robbed. Can't you see--can't you guess the way they have been lying to you?"

"Of course I can," I said coolly; "but when one's between the Devil and Dartmoor, I prefer the Devil every time. I don't enjoy being cheated, but it's much more pleasant than being starved or flogged."

She leaned forward, holding the edge of the table with her hands.

"There's no need for either. As I've told you, in a few hours from now we can be away from England with money enough to last us for our lives. Do you know what your invention is worth? Do you know what use they mean to make of it?"

"I imagine they hope to sell it," I answered. "It wouldn't be difficult to find a customer."

"Difficult!" She lowered her voice to a quick eager whisper. "They have got a customer. The best customer in Europe. A customer that will pay anything in the world for such a secret as yours."

I gazed at her with a carefully a.s.sumed expression of amazement and dawning intelligence.

"Good Lord, Sonia!" I said slowly; "do you mean--?"

She made an impatient movement with her hands. "Listen! I am going to tell you everything. What's the good of you and I beating about the bush?" She paused. "We are spies," she said quite simply, "professional spies. Of course it sounds absurd and impossible to you--an Englishman--but all the same it's the truth. You don't know what sort of man Dr. McMurtrie is."

"I appear to be learning," I observed.

"He has been a friend of my father's for years. They were in Russia together at one time--and then Paris, Vienna--oh, everywhere. It has always been the same; in each country they have found out things that other Governments have been willing to pay for. At least, the doctor has. The rest of us, my father, myself, Hoffman"--she shrugged her shoulders--"we are his puppets, his tools. Everything we have done has been planned and arranged by him."

There was a short silence.

"How long have you been here?" I asked. "What brought you to England?"

"We have been here just over three years," she answered slowly. "There was a man in London that Dr. McMurtrie and my father wanted to find.

Eight years ago he betrayed them in St. Petersburg."

A sudden idea--so wild as to be almost incredible--flashed into my mind.

I moistened my lips. "Who was he?" I asked steadily.

She shook her head. "I don't know his name. I only know that he is dead. I think Dr. McMurtrie would kill any one who betrayed him--if he could."

I crossed the room and sat down on the edge of the bed. I felt strangely excited.

"And after that," I said quietly, "I suppose the doctor thought he might as well stop here and do a little business?"

"I think it was suggested to him from Berlin. He had sent them all sorts of information when we were in Paris, and, of course, as things are now, they were still more anxious to get hold of anything about the English army or navy." She paused. "What they specially wanted were the plans of the Lyndon-Marwood torpedo."

"Yes," I said. "I dare say they did. A lot of people have wanted them, but unfortunately they're not for sale."

Sonia laughed softly. "The exact price we paid for them," she said, "was twelve thousand pounds."

I sat up with a jerk. This time my surprise was utterly genuine.

"You bought them!" I said incredulously. "Bought them from some one in the Admiralty?"

Again Sonia shook her head. "Don't you remember what you read in the _Daily Mail_ about the robbery at your offices in Victoria Street?"

I stared at her for a second, and then suddenly the real truth dawned on me.

"So George sold them to you?" I said.

She nodded. "Ever since you went to prison the business has been going to pieces. He wanted money badly--very badly indeed. Dr. McMurtrie found this out. He found out too that there was a copy of the plans in the office, and--well, you can guess the rest. The burglary, of course, was arranged between them. It was meant to cover your cousin in case the Government found out that the Germans had got hold of the plans."

"And have they found out?" I asked.