For an instant I stared at this cryptic message in bewilderment; then suddenly the recollection of my final instructions to Gertie ’Uggins rushed into my mind.

So Sonia had gone to the police, or had at least contrived to send them a message which served the same purpose.  Their visit to Edith Terrace was probably explained by the fact that she had given them both addresses so as better to establish the truth of her story.  Anyhow the murder was out, and with a new and not unpleasant thrill of excitement I crushed up Gertie’s wire in my hand and tore open McMurtrie’s letter.

“DEAR MR. NICHOLSON,

“I have been away on business and have only just received your letter, otherwise I should have come to see you this afternoon.  In the first place allow me to congratulate you most heartily on your success, of which personally I was never in any doubt.

“For the moment I have left the Hotel Russell, and am staying with some friends in Sheppey.  I shall run up the river in their launch early tomorrow morning, as I believe there is a small creek close to the hut where we can put in.

“Please have a specimen of the powder ready, and if it is possible I should like you to arrange for an actual demonstration, as I shall have a friend with me who is already considerably interested in our little company, and would be prepared to put up further capital if convinced of the merits of your invention.

“You can expect us about high water, between half-past nine and ten.

“Your sincere friend,

“L.J.  McMURTRIE.”

As I read the signature McMurtrie’s smiling mask-like face seemed suddenly to rise up in front of me, and all my old instincts of distrust and repulsion came to keep it company.  So he was at the bungalow, and in little over an hour he would be here—­he and the mysterious friend who was “already considerably interested in our little company.”  I smiled grimly at the phrase; it was so characteristic of the doctor; though when he wrote it he could little have guessed how thoroughly I should be able to appreciate it.

He was also equally ignorant of the complications introduced into the affair by Sonia.  Unless I had been altogether misled by Gertie’s message, it was probable that the police were even now on their way to arrest me, just as McMurtrie’s launch was most likely setting out from the little creek under the bungalow.  There seemed every prospect of my having a busy and interesting morning.

At this point in my reflections I looked up, and found Charles eyeing me with an air of respectful patience.  I took some money out of my pocket, and selecting a ten-shilling piece placed it in his grubby but not unwilling palm.

“You are a most useful boy, Charles,” I said, “and you can keep the change as usual.”

He pocketed the coin with a gratified stammer.

“You ain’t ’ad time to make no fireworks yourself, sir?” he hazarded, after a short pause.