“It is easy to trace a connection when one knows all the facts,” he said at length, “but it seems to me that you have the materials from which to form a conjecture.  Perhaps I am wrong, but I think, when you have had more experience, you will find yourself able to work out a problem of this kind.  What is required is constructive imagination and a rigorous exactness in reasoning.  Now, you are a good reasoner, and you have recently shown me that you have the necessary imagination; you merely lack experience in the use of your faculties.  When you learn my purpose in having these things made—­as you will before long—­you will probably be surprised that their use did not occur to you.  And now let us go forth and take a brisk walk to refresh ourselves (or perhaps I should say myself) after the day’s labour.

CHAPTER XI

THE AMBUSH

“I am going to ask for your collaboration in another case,” said Thorndyke, a day or two later.  “It appears to be one of suicide, but the solicitors to the ‘Griffin’ office have asked me to go down to the place, which is in the neighbourhood of Barnet, and be present at the post-mortem and the inquest.  They have managed to arrange that the inquest shall take place directly after the post-mortem, so that we shall be able to do the whole business in a single visit.”

“Is the case one of any intricacy?” I asked.

“I don’t think so,” he answered.  “It looks like a common suicide; but you can never tell.  The importance of the case at present arises entirely from the heavy insurance; a verdict of suicide will mean a gain of ten thousand pounds to the ‘Griffin,’ so, naturally, the directors are anxious to get the case settled and not inclined to boggle over a little expense.”

“Naturally.  And when will the expedition take place?” I asked.

“The inquest is fixed for to-morrow—­what is the matter?  Does that fall foul of any arrangement of yours?”

“Oh, nothing of any importance,” I replied hastily, deeply ashamed of the momentary change of countenance that my friend had been so quick to observe.

“Well, what is it?” persisted Thorndyke.  “You have got something on.”

“It is nothing, I tell you, but what can be quite easily arranged to suit your plans.”

“Cherchez la—­h’m?” queried Thorndyke, with an exasperating grin.

“Yes,” I answered, turning as red as a pickled cabbage; “since you are so beastly inquisitive.  Miss Gibson wrote, on behalf of Mrs. Hornby, asking me to dine with them en famille to-morrow evening, and I sent off an acceptance an hour ago.”

“And you call that ’nothing of any importance’!” exclaimed Thorndyke.  “Alas! and likewise alackaday (which is an approximately synonymous expression)!  The age of chivalry is past, indeed.  Of course you must keep your appointment; I can manage quite well alone.”