Hetherwick followed his companion across the Strand, into the Adelphi, and to the house they wanted—an old Adams mansion, now divided into flats. Matherfield did not take the trouble to ascend to the upper regions; he sought and found a caretaker and put a question to him. The man shook his head.  
"Dr. Ambrose, sir?" he replied. "Oh, yes, Dr. Ambrose lives here—38. But he ain't in, sir—ain't at home, in fact. He's been away three weeks or so—don't know where he is."
 
With a meaning look at Hetherwick, Matherfield drew the caretaker aside and talked to him for a few moments; the man presently turned and went downstairs to the basement from which they had summoned him.
 
"That's all right," remarked Matherfield, with a wink. "He's going to let us into Ambrose's flat. Didn't I tell you we shouldn't find Ambrose here? Not he! I should say he's off!"
 
"Supposing he returns—while we're here?" asked Hetherwick.
 
"Wish he would!" chuckled Matherfield. "Nobody I want to see more! If he did, why, I should just ask him to take a little walk with me—to explain a few matters. But he won't! Here's the man. We'll go up."
 
The caretaker reappeared with a bunch of keys and led the way to a flat at the top of the old house. He unlocked a door and stood aside.
 
"You needn't wait," said Matherfield. "I'll shut the place up again when we leave and let you know. All right."
 
He walked in, with Hetherwick at his heels, as soon as the caretaker had gone, and, once inside, closed the door carefully upon himself and his companion. But Hetherwick, after a first glance at the sitting-room into which they had entered, a somewhat untidy, shabbily furnished place, went straight to the hearth and pointed to a framed photograph, time-stained and faded, which hung over the mantelpiece.
 
"There's a striking and significant piece of evidence—at once!" he exclaimed. "Do you know what that is, Matherfield?"
 
Matherfield looked in the direction indicated, and shook his head.
 
"Not the slightest idea!" he answered. "I see it's a photograph of some old church or other—that's all."
 
"That's the famous Parish Church of Sellithwaite!" said Hetherwick. "One of the very finest in England! I had a look at it—only a mere look—when I was down there. Now then, what's this man doing with a picture of Sellithwaite Parish Church in his rooms? Hannaford came from Sellithwaite!"
 
"That's a mighty significant thing, anyway," agreed Matherfield. "We're getting at something this morning!" He looked more carefully at the photograph. "Grand old building, as you say," he continued. "Of course, the mere fact of his having it put up there shows that he's some interest in it. Sellithwaite man, likely. But we'll find all that out. Now let's look round."
 
There was little to see, Hetherwick thought. The flat consisted of a sitting-room and bedroom and a small bathroom. The furniture was plain, old, rather shabby; the whole place suggested that its occupant was not over well-to-do; the only signs of affluence to be seen were manifested in the toilet articles on the dressing-table, in a luxurious, if well-worn, dressing-gown which hung on the rail of the bed, and in the presence of carefully folded and pressed garments laid out in the bedroom. There were a few books, chiefly medical treatises, in shelves in the sitting-room; a few personal pictures, mainly of college and school groups, on the walls; and a desk in the centre, littered with more books, writing materials, and papers. Matherfield began to turn them over.
 
"See that?" he exclaimed suddenly, pointing to a movable calendar which stood on the top ledge of the desk. "Notice the date? March 18th! That's the day on which Hannaford got his quietus. At least, strictly speaking, it was the day before. Hannaford actually died on the nineteenth—about—what was it?—very early in the morning, anyway. What's one to gather from this?—that Ambrose hasn't been here since the eighteenth. So—hallo!"
 
Turning over the loose papers that lay about the blotting-pad, he had suddenly lighted upon a telegram; just as suddenly he thrust it into Hetherwick's hands.
 
"Look at that!" he exclaimed. "Now, that is a find! Biggest we've ever had—so far!"
 
Hetherwick read the apparently innocent message.
 
 
"All right. Will meet you Victoria bookstall this evening as suggested.
 
"Hannaford."
 
 
"See the date?" said Matherfield excitedly. "March 18th! Now we've got at it! Ambrose was the man that met Hannaford at Victoria, the tall, muffled-up man that Ledbitter saw! That's—certain!"
 
"Seems so," agreed Hetherwick. He was still studying the telegram. "Sent off from Fleet Street twelve-fifteen that day," he muttered. "Yes—there doesn't seem much doubt about this. I wonder who this man Ambrose is?"
 
"We'll soon get to know something about that, Mr. Hetherwick!" exclaimed Matherfield briskly. "Now, I'm just going to put that wire in my pocket, lock up this flat again, have another word or two with that caretaker chap, and go in search of the information you refer to. Come with me! Later, I shall get a search warrant, and make a thorough examination of this flat. Let's be moving."
 
Downstairs again, Matherfield called up the caretaker.
 
"You say Dr. Ambrose has been away for a bit?" he asked. "Is there anything unusual in that?"
 
"Well, not so very," answered the man. "Ever since he came here, two or three years ago, he's been used to going away for a while. I believe he used to go over to Paris. But I never remember him being away more than a week at a time before."
 
"Evidently he's a doctor," suggested Matherfield. "Did he ever have patients come to see him here?"
 
The caretaker shook his head.
 
"No," he replied. "He never had anybody much come to see him here—never remember anybody, unless it was somebody he brought in at night for a smoke, you know. He generally went out early in a morning, and came home late—very late."
 
"What about his meals?" asked Matherfield.
 
"He'd no meals here—unless he made himself a cup of coffee or so in a morning," said the caretaker. "All his meals out—breakfast, too. Sundays as well as weekdays. We saw very little of him."
 
"Who does up his rooms—makes the bed and so on?" inquired Matherfield.
 
"My wife," answered the caretaker. "She does all that."
 
"And she hasn't had anything to do for—how long?"
 
"Well, it'll be three weeks, I'm sure. He never used to say anything at any time when he went off—just went. He'd call downstairs when he came back and let us know he was back, d'ye see? But we never thought he'd be as long away as this, this time. It was only this morning, just before you came, that my missus said to me that it seemed queer."
 
"Why queer?"
 
"Because he's taken nothing with him. However short a time he might be away before, he always took a suit-case, clean linen, shaving things, so on—he was a very particular gentleman about his appearance—always dressed like a swell and had a clean shirt every day; used to have a nice heavy washing-bill, anyhow!"
 
"Did he seem to be pretty well supplied with money?" asked Matherfield. "Or—the opposite?"
 
"Couldn't rightly say," replied the caretaker. "Always paid his rent, and us, and the washing regular, but as for anything else, why, we'd no means of knowing. Of course, as I tell you, he always looked the gentleman."
 
"I see!" said Matherfield. "All right—you'll see me again this afternoon."
 
He strode away towards the Strand, and there ushered Hetherwick into the first empty taxi-cab they met.
 
"Where now?" asked Hetherwick as Matherfield followed him into the cab after a word to its driver.
 
"We're going now, sir, to Hallam Street, to the offices of the General Medical Council," answered Matherfield promptly. "I've had experience of inquiring into the antecedents of medical men before, and I know where to find out all about any of 'em. I'm going to find out all about this Dr. Charles Ambrose—that is, of course, if he's an English doctor."
 
"Probably he isn't," remarked Hetherwick, "any more than Baseverie is."
 
"Ah, Baseverie!" exclaimed Matherfield. "I'd forgotten that man for the time being! Well, while we're about it, we'll see if we can unearth a bit of information concerning him. We've done a bit of good work this morning, ye know, Mr. Hetherwick!" he went on, rubbing his hands with satisfaction. "We've practically made certain that Ambrose was the man who met Hannaford at Victoria, and we're sure he's the man to whom Macpherson supplied the bottle in which the poison was discovered at Granett's room. And now we'll hope for a bit more illumination in the darkness!"
 
Hetherwick presently found himself closeted with Matherfield and a grave official who, after seeing Matherfield's credentials and listening to his reasons for his visit o............