“I did know,” said Lettice. “I believe it was just about now.”

“She sailed yesterday,” said Thrush, impressively; “and your brother, if it was your brother, talked a good deal about her to this man. He told him all about your having always been in favour of it, Miss Upton, and his father not. I’m bound to say it sounds as though it may have been the boy.”

Thrush seemed to be keeping something back; but the prime and absorbing question of identity prevented the others from noticing this.

“It must have been!” cried Mr. Upton. “Who was the man, and where exactly did he see him?”

“First on Thursday morning, and last on Thursday night. But perhaps I’d better tell you about my informant, since we’ve only his word for Thursday, and only his suspicions as to what has happened since. In the first place he’s a semi-public man, though I don’t suppose you know his name. It’s Baumgartner—Dr. Otto Baumgartner—a German scientist of some distinction.”

The ironmaster made a remark which did him little credit, and Thrush continued with some pride: “There was some luck in it, of course, for he was the very first man I struck who’d bought d’Auvergne Cigarettes since Wednesday; but I was on his doorstep well within twenty-four hours of hearing that your son was missing; and you may chalk that up to A. V. M.! I might have been with him some hours sooner still, but I preferred to spend them getting to know something about my man. I tried his nearest shops; perfect mines! One was a chemist, who didn’t know him by sight, and had never heard of the cigarettes, but remembered being asked for them by an elderly gentleman last Thursday morning! That absolutely confirmed my first suspicion that Baumgartner himself was not the asthmatic; if he had been, the nearest chemist would have known all about him. Yet he had gone to the nearest chemist first!”

“The nearest butcher was next door; but he was so short about Baumgartner that I scented a true-green vegetarian. It was a false scent, Mr. Upton; not to mention the baker and the candlestick-maker, there’s a little restaurant in the same row, which was about the fifth place where I began by asking if they knew where a Dr. Baumgartner lived in that neighbourhood. The little Italian boss was all over me on the spot! The worthy doctor proved to be his most regular customer, having all his meals sent in hot from the restaurant in quite the Italian manner. I don’t suppose you see how very valuable this was to me. Germans love Italy, the little man explained; but I said that was the one point on which I should never yield to Germany—and I thought I was going to be kissed across the counter! It seems the good doctor lives alone with his niece (not always even her), and keeps no servants and never entertains. Yet on Friday, for the first time since the arrangement was made, the old chap went to the restaurant himself to complain of short commons; there had not been enough for them to eat on the Thursday night!”

“Had they been alone?” asked Mr. Upton, with a puzzled face.

“That’s the whole point! My little Florentine understood they were, but I deduced one extra, and then conceived a course that may astonish you. It was the bold course; but it nearly always pays. I lunched at my leisure (an excellent Chianti my little friend keeps) and afterwards went round and saw the doctor himself. The niece opened the door—I wish I’d seen more of her—but she fetched her uncle at once and I begged for an interview on an urgent matter. He consented in a way that, I must say, impressed me very favourably; and the moment we were alone I said, ‘I want to know, Doctor, who you bought those asthma cigarettes for last Thursday!’”

“That took him aback, but not unduly; so then I added, ‘I’m an inquiry agent with a very delicate case in hand, and if you’ll tell me it may solve at heart-breaking a mystery as I’ve ever handled.’ Is was treating him like a gentleman, but I believe in that; there’s no shorter cut to whether a man is one or not.”