As it was, I had very little doubt that the rat of a man I had chanced to protect in the railway carriage was no other than the extraordinarily expert thief who had relieved du Laurier of the Duchess's necklace.
Following out a theory which I worked up as I walked, I thought it probable that the fellow had been helped by confederates whom he had contrived to dodge, evading them and sneaking off to London in the hope of cheating them out of their share of the spoil.

Followed by them, dreading their vengeance, I fancied him flitting from one hiding-place to another, not daring to separate himself from the jewels; at last determining to escape, disguised, from England, where the scent had become too hot; reserving a first-class carriage in the train to Dover, and travelling with a golfer's kit; struck with panic at the last moment on seeing the very men he fled to avoid, close on his heels, and opening the door of his reserved carriage with a railway key.
All this was merely deduction, for so far as I had seen, "J.M.'s" travelling companions hadn't even accosted him.

Still, the theory accounted for much that had been puzzling, and made it plausible that a man should be desperate enough to trust his treasure to a stranger (known only through "photos in the newspapers") rather than risk losing it to those he had betrayed.
I resolved to use all my powers of diplomacy to extract from "J.M." the case containing the treaty before he learned that he was not to receive the diamonds in its place; and I had no more than vaguely mapped out a plan of proceeding before I arrived in the Avenue Morot.

Thence I soon found my way into the Rue de la Fille Sauvage, a mean street, to which the queer name seemed not inappropriate.

The house I had to visit was an ugly big box of a building, with rooms advertised to let, as I could see by the light of a street lamp across the way, which gleamed bleakly on the lines of shut windows behind narrow iron balconies.
The large double doors, from which the paint had peeled in patches, were closed, but I rang the bell for the concierge; and after a delay of several minutes I heard a slight click which meant that the doors had opened for me.