"When I had fixed him up, he asked me to do him a small favour. From inside his tunic he pulled out a long stiff envelope, bearing no address but the number 30 in big red letters. It was secured at both ends with black wax bearing the imprint of a curious and complicated seal. "'A gentleman left this behind in the cab today, sir,' said the man--'perhaps the one who was with me when I had the spill, and I've got no means of tracing him; but he may be able to trace _me_ if he happened to notice my number, or he may advertise. It evidently contains something valuable.' "'Then why not take it to Scotland Yard?' I asked. 'Isn't that the proper course?' "'It is,' he admitted; 'but here's the point: if the owner reclaims it from Scotland Yard he's less likely to dub up handsome than if he gets it direct from me!' "I laughed at that, for the soundness of the argument was beyond dispute. 'But what on earth do you want to leave it with _me_ for?' I asked." "'Self-protection,' was the reply. 'They can't say I meant to pinch it! Whereas, directly there's any inquiry I can come and collect it and get the reward; and your word will back me up if any questions are asked; that's if you don't mind, sir.' "I told him I didn't mind in the least, and accordingly I sealed the envelope in a yet larger one which I addressed to the Lost Property Office and put into a private drawer of my bureau. 'You will have no objection,' I said, 'to this being posted if it isn't reclaimed within a reasonable time?' "He said that would be all right and departed--since which moment I have not set eyes upon him. I now come to the sequel, or what I have just recognized to be the sequel." Stuart's agitation grew more marked and it was only by dint of a palpable effort that he forced himself to resume. "On the evening of the following day a lady called professionally. She was young, pretty, and dressed with extraordinary elegance. My housekeeper admitted her, as I was out at the time but momentarily expected. She awaited my return here, in this room. She came again two days later. The name she gave was an odd one: Mademoiselle Dorian. There is her card,"--Stuart opened a drawer and laid a visiting-card before Dunbar--"no initials and no address. She travelled in a large and handsome car. That is to say, according to my housekeeper's account it is a large and handsome car. I personally, have had but an imperfect glimpse of it. It does not await her in front of the house, for some reason, but just around the corner in the side turning. Beyond wondering why Mademoiselle Dorian had selected me as her medical advisor I had detected nothing suspicious in her behaviour up to the time of which I am about to speak. "Last night there was a singular development, and to-night matters came to a head."