“I think that she simply walked past us—­probably on the other side of the road—­as we stood waiting for the omnibus, and turned up Kennington Park Road.  She probably guessed that we were waiting for the omnibus and walked up the road in the direction in which it was going.  Presently the omnibus would pass her, and there were you in full view on top keeping a vigilant look-out in the wrong direction.  Then she would quicken her pace a little and in a minute or two would arrive at the Kennington Station of the South London Railway.  In a minute or two more she would be in one of the electric trains whirling along under the street on which your omnibus was crawling.  She would get out at the Borough Station, or she might take a more risky chance and go on to the Monument; but in any case she would wait for your omnibus, hail it and get inside.  I suppose you took up some passengers on the way?”

“Oh dear, yes.  We were stopping every two or three minutes to take up or set down passengers; and most of them were women.”

“Very well; then we may take it that when you arrived at the Mansion House, Mrs. Schallibaum was one of your inside passengers.  It was a rather quaint situation, I think.”

“Yes, confound her!  What a couple of noodles she must have thought us!”

“No doubt.  And that is the one consoling feature in the case.  She will have taken us for a pair of absolute greenhorns.  But to continue.  Of course she travelled in your omnibus to Kensington—­you ought to have gone inside on both occasions, so that you could see every one who entered and examine the inside passengers; she will have followed you to Endsley Gardens and probably noted the house you went to.  Thence she will have followed you to the restaurant and may even have lunched there.”

“It is quite possible,” said I.  “There were two rooms and they were filled principally with women.”

“Then she will have followed you to Sloane Street, and, as you persisted in riding outside, she could easily take an inside place in your omnibus.  As to the theatre, she must have taken it as a veritable gift of the gods; an arrangement made by you for her special convenience.”

“Why?”

“My dear fellow! consider.  She had only to follow you in and see you safely into your seat and there you were, left till called for.  She could then go home, make up for her part; draw out a plan of action, with the help, perhaps, of Mr. Weiss, provide herself with the necessary means and appliances and, at the appointed time, call and collect you.”

“That is assuming a good deal,” I objected.  “It is assuming, for instance, that she lives within a moderate distance of Sloane Square.  Otherwise it would have been impossible.”

“Exactly.  That is why I assume it.  You don’t suppose that she goes about habitually with lumps of prepared sugar in her pocket.  And if not, then she must have got that lump from somewhere.  Then the beads suggest a carefully prepared plan, and, as I said just now, she can hardly have been made-up when she met us in Kennington Lane.  From all of which it seems likely that her present abode is not very far from Sloane Square.”