“And you believe McMurtrie never meant to keep his word to me?” I asked.

She laughed again scornfully.  “If you knew him as well as I do, you wouldn’t need to ask that.  He would simply have disappeared with the money and left you to rot or starve.”

I took out my case, and having given Sonia a cigarette, lit one myself.

“It’s an unpleasant choice,” I said, “but I gather there’s a possible alternative.”

She lighted her own cigarette and threw away the match.  Her dark eyes were alight with excitement.

“Listen,” she said.  “All the Germans want is the secret.  Do you suppose they care in the least whom they get it from?  You have only got to prove to them that you can do what you say, and they will pay you the money just as readily as they would the doctor.”

There was a magnificent simplicity about the idea that for a moment almost took my breath away.

“How could I get in touch with them?” I asked.

She leaned forward again, and lowered her voice almost to a whisper.

“I can take you now—­now right away—­to the two men who are in charge of the whole business.  I know that they have an absolutely free hand to make the best terms they can.”

“Who are they?” I demanded, with an eagerness I made no attempt to hide.

“Their names are Seeker and von Bruenig, and they’re living in a small bungalow on Sheppey.  They are supposed to be artists.  As a matter of fact, von Bruenig is a captain in the Germany Navy.  I don’t know who the other man is; I think he has been sent over specially about the powder.”

Her statement fitted in so exactly with what I had already found out from Latimer and Gow, that I hadn’t the remotest doubt she was telling me the literal truth.  Of its importance—­its vital importance to England—­there could be no question.  I felt my heart beating quickly with excitement, but the obvious necessity for fixing on some scheme of immediate action kept my brain cool and clear.  The first thing was to gain a moment or two to think in.

“You realize what all this means, Sonia?” I said.  “You’re quite prepared to throw over your father and McMurtrie?  You know how the doctor deals with people who betray him—­when he gets the chance?”

“I am not afraid of them,” she answered defiantly.  “They are nothing to me; I hate them both—­and Hoffman too.  It’s you I want.  You are the only man I ever have wanted.”  She paused, and I saw her breast rising and falling rapidly with the stress of her emotion.  “We will go away together—­somewhere the other side of the world—­America, Buenos Ayres—­oh, what does it matter where?—­there are plenty of places!  What does anything matter so long as we love each other!”

She half rose to her feet, but I jumped up first.

“One moment, Sonia,” I said.  “Let me think.”

Thrusting my hands in my pockets, I strode across the room, and pulling up in front of the little window, stared out across the marsh.  As I did so, I felt as if some one had suddenly placed a large handful of crushed ice inside my waistcoat.  About two hundred yards away, strolling cheerfully and unconcernedly towards the hut, was the charming but painfully inopportune figure of Joyce.