“Different habits of touch, spacing, speed, arrangement, and punctuation all may also tend to show that a particular piece of writing was or was not done by one operator.  In other words, typewriting individuality in many cases is of the most positive and convincing character and reaches a degree of certainty which may almost be described as absolute proof.  The identification of a typewritten document in many cases is exactly parallel to the identification of an individual who precisely answers a general description as to features, complexion, size, and in addition matches a long detailed list of scars, birthmarks, deformities, and individual peculiarities.”

Together we three began an exhaustive examination of the letters, and as Kennedy called off the various characteristics of each type on the standard keyboard we checked them up.  It did not take long to convince us, nor would it have failed to convince the most sceptical, that both had come from the same source and the same writer.

“You see,” concluded Kennedy triumphantly, “we have advanced a long step nearer the solution of at least one of the problems of this case.”

Miss Kendall had evidently been thinking quickly and turning the matter over in her mind.

“But,” she spoke up quickly, “even that does not point to the same person as the author—­not the writer, but the author—­of the three pieces of writing.”

“No indeed,” agreed Craig.  “There is much left to be done.  As a matter of fact, there might have been one author, or there might have been two, although all the mechanical work was done by one person.  But we are at least sure that we have localized the source of the writing.  We know that it is from the Montmartre that the letter came.  We know that it is in some way that that place and some of the people who frequent it are connected with the disappearance of Betty Blackwell.”

“In other words,” supplied Clare, “we are going to get at the truth through that Titian-haired stenographer.”

“Exactly.”

Clare had risen to go.

“It quite takes my breath away to think that we are really making such progress against the impregnable Montmartre.  At various times my investigators have been piecing together little bits of information about that place.  I shall have the whole record put together to-night.  I shall let you know about it the first thing in the morning.”

The door had scarcely closed when Kennedy turned quickly to me and remarked, “That girl has something on her mind.  I wonder what it is?”

XII

The “Portrait parle”

What it was that Clare Kendall had on her mind, appeared the following day.

“There’s something I want to try,” she volunteered, evidently unable to repress it any longer.  “I have a plan—­or half a plan.  Don’t you think it would be just the thing, under the circumstances, to ring up District Attorney Carton, tell him what we have accomplished and take him into our confidence?  Perhaps he can suggest something.  At any rate we have all got to work together, for there is going to be a great fight when they find out how far we have gone.”