We hastily resumed our uptown journey.

“What do you think it is?” I asked.  “About Betty Blackwell?”

Kennedy shook his head non-committally.  “I don’t know.  But he has some of his county detectives watching Dorgan and Murtha in that Black Book case, I know.  They are worried.  It doesn’t look as though they, at least, had the record—­that is, if Langhorne has really lost it.”

I wondered whether Langhorne might not, after all, as Kennedy had hinted, have concealed it elsewhere.  The activity of Dorgan and Murtha might indicate that they knew more about the robbery than appeared yet on the surface.  Had they failed in it?  Had they been double-crossed by the man they had chosen for the work, assuming that they knew of and had planned the “job”?

The safe-breaking and the way Langhorne took it had served to complicate the case even further.  While we had before been reasonably sure that Langhorne had the book, now we were sure of nothing.

IV

THE ANONYMOUS LETTER

“What do you make of that?” inquired Carton half an hour later as he met us breathlessly at the laboratory.

He unfolded a letter over which he had evidently been puzzling considerably.  It was written, or rather typewritten, on plain paper.  The envelope was plain and bore no marks of identification, except possibly that it had been mailed uptown.

The letter ran: 

Dear sir: 

Although this is an anonymous letter, I beg that you will not consider it such, since it will be plain to you that there is good reason for my wishing to remain nameless.

I want to tell you of some things that have taken place recently at a little hotel in the West Fifties.  No doubt you know of the place already—­the Little Montmartre.

There are several young and wealthy men who frequent this resort.  I do not dare tell you their names, but one is a well-known club-man and man about town, another is a banker and broker, also well known, and a third is a lawyer.  I might also mention an intimate friend of theirs, though not of their position in society—­a doctor who has somewhat of a reputation among the class of people who frequent the Little Montmartre, ready to furnish them with anything from a medical certificate to drugs and treatment.

I have read a great deal in the newspapers lately of the disappearance of Betty Blackwell, and her case interests me.  I think you will find that it will repay you to look into the hint I have given.  I don’t think it is necessary to say any more.  Indeed it may be dangerous to me, and I beg that you will not even show this letter to anyone except those associated with you and then, please, only with the understanding that it is to go no farther.

Betty Blackwell is not at this hotel, but I am sure that some of those whose wild orgies have scandalized even the Little Montmartre know something about her.