It was after nine when Plummer returned. The rector had just rejoined Hewitt in the study, having left poor Miss Creswick, utterly broken down, in her room, in charge of a scarcely less terrified servant. Plummer tapped, and pushed the study door open.

"That's done clean and sure enough," he said, with professional calmness. "And he's a cool hand, is that Dr. Lawson. But have you found anything more? We shall want all we can get."

"We shall," Hewitt assented, "and we shall find more than we've got now, or I'm grievously mistaken. But tell me first what you've done."

He removed the blotting pad, on which the paper ashes still lay, and very carefully shut it away in a wide drawer where no draught could disturb it; he also shut another drawer which stood open.

"We had no difficulty in finding Dr. Lawson," Plummer began. "We met him, in fact, leaving his surgery. I went back with him into the gas-light, and there put it to him plump. Well, he was staggered, badly. Any man would be, of course. But he pulled himself together wonderfully soon, and the first thing he said was that he was just on his way to Mason's house. I thought at first, of course, that he meant to deny that he had been there already, and I gave him the usual warning about what he said being used in evidence. But he went on, and I've got it all safely noted. He admitted that he had been here, at about seven o'clock or just before, and he said he came because Mr. Mason sent for him. That doesn't seem likely, does it, on the facts as we know them?"

"Why, no," said the rector. "The last time he was here he was ordered out, and I know of no reason why he should have been asked to come to-day. We must ask if anybody was sent."

"I have asked," replied Plummer, "just now, and none of the servants was sent. But Lawson's story is that he was sent for and came, though he said he shouldn't say what Mason wanted to see him about till he knew more of the case. Looks as though he hadn't quite got his story ready yet, doesn't it? He had thought over the point about not being seen to go away, though; he said he had let himself out at about half-past seven, being familiar with the ways of the house. And he said that Mason was rather unwell—nervously upset—when he left him, but that was all."

"It's terrible," said the rector, "terrible. It seems impossible to believe it of young Lawson; and yet—and yet!" And then after a pause—"Good heavens!" he burst out again. "Why, I only realise it now! There is the other crime, too! Denson! Two murders! Two—and most certainly by the same hand! Mr. Plummer, I can't believe it! Oh, there's more behind, more behind, Mr. Hewitt."

"There is more," said Hewitt, "as you will see when I tell you the little I have been able to ascertain. There is more behind, though I see little of it yet. First——"

There was a sharp knock at the front door, followed by a ring, muffled in the distant kitchen. Hewitt started up. "Who is this late visitor at this unvisited house?" he said. "If it is the police, well enough. But if anybody else—anybody—you may call me Doctor, or anything you please, except Martin Hewitt. Don't forget that!"

There were hurried steps in the hall, a question or two, and the study door was pushed open. Two servants—they would not venture from the kitchen singly this dreadful night—made a confused announcement of "Mr. Myatt," and were instantly pushed aside by Mr. Myatt himself, anxious and agitated.

The late Mr. Mason's closest scientific friend was a palish, black-bearded man, of above middle height, with stooping shoulders and a very quick pair of eyes. There was something about his face that somehow reminded Hewitt of portraits he had seen of John Knox, and yet it was not such a face as his; it seemed oddly unlike in its very likeness.

"What is this dreadful news, Mr. Potswood?" he cried. "I heard people talking in the next street on my way home. Is it true? But the servants have told me so. They say our poor friend—but there has been an arrest, hasn't there?"

The rector nodded gravely.

"And who? Tell me about it, Mr. Potswood—tell me!"

"I think I must see how Miss Creswick is doing," said Hewitt, speaking across to Plummer and making for the door.

"Certainly, doctor, certainly!" answered Plummer with a nod.

Hewitt closed the door behind him, leaving the rector in the full tide of his account of the day's events; but Hewitt's way took him to the kitchen, where the servants were cowering and whispering together, frightened and bewildered.

"Is there any paint or varnish of any sort in the place?" he asked sharply. "Give me anything there is—black, if possible—and a brush, quickly."

"There's—there's Brunswick black, sir, for the stove," said the cook.

"That will do; be quick. Oh, there's Gipps, the gardener! You're just the man I want, Gipps. Come and find me a board or a plank, quick as you please!" And Hewitt pushed the old gardener before him into the garden by the kitchen door.

A quarter of an hour later, Mr. Everard Myatt, having heard all that was to be told of his friend's terrible death and the arrest of Mr. Lawson, turned to go, meeting Hewitt at the study door on his way.

"And how is poor Miss Creswick by now, doctor?" he asked anxiously.

Hewitt shook his head. "No better than you could expect," he said, "but, on the whole, no worse. She mustn't be seen to-night, of course, but, perhaps, if you could call round in the morning with the rector——"

"Of course—of course! Poor girl—and Dr. Lawson suspected, too—what a terrible blow for her! Anything I can do, doctor, of course, as I said to Mr. Potswood—anything I can do I will do as gladly as such sad circumstances permit."

The rector had been coming to the door with Mr. Myatt, but Plummer, catching a sign from Hewitt, restrained him unseen, and Hewitt and the visitor walked into the hall together.

"They have put out the light, it seems," Hewitt said. "I wonder why—unless people from the crowd have been coming into the garden and staring in through the glass panels. I wonder if we can find the door-handle. Yes, here it is. Dark outside, too! Good-night—mind how you go on the steps!"

Mr. Myatt checked and stumbled in the dark porch, and reached quickly downward.

"There's a board standing across the porch," he said.

"A board?" replied Hewitt. "So there is. Let me move it, or it'll upset somebody. Good-night!"

Mr. Myatt strode off into the dark night, and Hewitt, noiselessly lifting the board he had himself placed in position, hastened back to the study.

He swung up the board, all sticky and shiny with Brunswick black, and laid it across a spread newspaper, on the table. There on the top, in the midst of the black varnish, were the prints of all five finger-tips of a hand, where Mr. Myatt had felt for the obstruction in the porch.

Hewitt opened the drawer he had shut a little while back, and took therefrom a sheet of writing-paper. And when, with the lens from his pocket, he began to examine that paper in comparison with the finger-marks on the board, Plummer and the rector could see that there were also two distinct finger-marks on the paper and one faint one—all red. Plummer came to look.

"What's this?" he said. "Was this what you were going to tell us about?"

Hewitt did not reply for a few moments, but continued his examination. Then he rose and turned to Plummer.

"You've still got that piece of paper in your pocket, I suppose," he said, "with the little red smudges of colour put there by the police surgeon?"

"Yes—here it is," and the detective took it from his waistcoat pocket.

"Thanks," said Hewitt. "Now, see here. That is a little of the red stuff taken from the mark on Denson's forehead a week ago, and found to consist of vermilion, oil and wax. You have seen the second impression of that awful mark on the forehead of your poor friend Mason, Mr. Potswood, to-night. This room has been searched for papers before we began, and papers have been burnt. In the search this drawer was opened—containing, as you see, nothing but a supply of new headed note-paper. The note-paper was hastily lifted to see if anything else lay beneath, and here, on the bottom sheet, these finger-marks were left in that same adhesive, freely marking red—a sort of stuff that sticks to and marks whatever it touches. The hand that lifted that paper was the hand that impressed that ghastly mark; and the hand that left its print on this black varnish was Mr. Everard Myatt's! Now compare the two!"

Plummer had snatched the lens, and was narrowly comparing the marks ere Hewitt had well finished speaking.

"They are!" he cried, as the rector bent excitedly over him. "They are the same! See—forefinger and middle finger—the same, every line!"

"I needn't tell you," pursued Hewitt, "certainly I needn't tell Plummer, that that is the most certain and scientific method of identification known. The police know that—and use it. But now there is some more. You saw me take that charred paper from the fire. Sometimes words may be read on charred paper—it depends on the paper and the ink. Most of the cinders were too much broken to yield any information, though we may try again by daylight. But one was suggestive. See it!" Hewitt very carefully pulled out the flat drawer that held the cinders.

"You see," he went on, "that one—this—is different from the rest. It has retained its original form better, and has been less broken, because of being of thicker paper. It is a crumpled envelope. Look at the flap—it has never been closed down. Moreover, on that same flap you may read in embossed letters, still visible, part of the name of this house. Plain inference—this was an envelope intended for a letter never sent, and so crumpled up and dropped into the waste-paper basket. But why should such an apparently unimportant thing as that be carefully brought from the waste-paper basket and burnt? Somebody was anxious that the smallest scrap of paper evidencing a certain correspondence should be destroyed. But look closely at the front of the envelope—the ink shows a rather lighter grey than the paper. The address is incomplete—at any rate, no more than some of the first line and a little of the second is at all visible now; but it is plain that the first line begins with an E. The letters immediately following are not distinct, but next there is a capital M beginning a name which is clearly Myatt or Myall. Now, that is why, when Myatt came here, I took the first steps to hand to get an impression of his finger-tips, in order to compare them with the marks on that paper."

"But why," asked the astonished rector, "why did he come back?"

"Nothing but a bold measure to see how things were going—he came as his own spy, that's all. He's a keen and dangerous man. Don't you remember telling me how he called on you yesterday, though you hardly knew him by sight, merely to ask you to persuade Mason to take a holiday? It struck me as a little odd at the time. He was pumping you, Mr. Potswood—he wanted to find what Mason had been saying! And he is not alone—plainly he is not alone, for poor Mason knew they were watching everywhere. But come—this is no time for speculation. Plummer—you must hold him safely—we'll pick up evidence enough when you've got him. I wouldn't leave it, Plummer—I'd take him to-night!"

"You're right—right, as usual, Mr. Hewitt," Plummer agreed. "More especially as the rector was—well, a little incautious in talking to him just now."

"I? What did I say?" Mr. Potswood asked, astonished. "I had no suspicions—how could I have——"

"No, Mr. Potswood," the detective replied, "you had no suspicions, and for that very reason, in the excitement of the narrative, you called Mr. Martin Hewitt by his right name at least twice! And after I had called him 'doctor,' too!" he added regretfully.

"Is that so?" asked Hewitt.

The poor rector was sadly abashed. "But I really wasn't aware of it, Mr. Hewitt!" he protested. "I hardly think I could—but, there, perhaps I did! Of course, if Inspector Plummer remembers it——"

"He'll be off!" exclaimed Hewitt. "With that hint, and finding the black stuff on his hands, he'll smell a rat instantly! Come, Mr. Potswood—you can show us the nearest way to his house, at any rate! Come—we may get him yet!"

But the good rector's slip of the tongue was fatal, and Myatt was not yet to meet the fate that fitted him. The house was not far—less than a mile away. It was a detached house, but quite a small one—smaller than Mason's. Plummer blocked every exit with a man, but his caution was wasted. Myatt was gone.

There was the house and the furniture and two servants, just as it might have been any day in the year when Myatt was out for an hour. But now he was out for good. The police watched and waited all night, and all the next day; they waited and watched for a week, and the house was under observation after that, but Myatt never returned. He had made his plans, it was plain, for just such a flight, whenever the necessity might arise; and when he was assured that danger threatened, he simply vanished in the dark of a London night. Search brought no information—not a scrap of telltale paper lay in Calton Lodge—not a letter, not a line. Though, indeed, the police were to see more of Myatt's work yet—and so was Hewitt.

Dr. Lawson's detention did not last the night out. The unhappy Mason had indeed sent to him, by a chance messenger, having grown desperate in long waiting for the return of Gipps from the rectory. Mason was ready to call in any aid, to recall any of the friendships he had sacrificed in the past. But Lawson was long in coming, having received the note after a long professional round, and when at last he arrived, Mason was a little reassured by the promise of Hewitt's visit. Therefore, he did not tell the doctor so much as he might have done. Nevertheless, he talked wildly and vaguely, so that Dr. Lawson feared some disturbance of his reason. The doctor quieted and soothed him, however, and when he left he promised to return after his consultation hour at the surgery was over. He must have been watched away from the house, and then the blow fell that sealed for ever the lips of Jacob Mason.

Poor Miss Creswick was taken from the old house in which she could no longer remain, and for a few months she stayed at the rectory, tended lovingly by the rector's excellent wife—stayed there, in fact, till her wedding-day, which took place early the next year; so that for her and Dr. Lawson the tragedy ended in happiness, after all.

"God forgive me," cried the rector in the grey of the morning, when it became clear that Myatt had escaped—"God forgive me! Through my stupidity a horrible creature has been set loose in the world to work his diabolical will afresh!"

"Never mind," said Hewitt. "It was not stupidity, Mr. Potswood—nothing but your openness of character. You were not trained to the cunning that we must use in my profession. And there will be more than Myatt to take—he was not alone! It is plain that Mason was found to be wavering in whatever horrible allegiance he had bound himself, and he was watched. No, Myatt was not alone!"

"No, I fear not," replied the clergyman. "I fear not: there is horrible mystery still. The watching and besetting that terrified him so much; the fact that he seems to have yielded up his life without a struggle—and that with help so near; and the connection—what could it have been?—between Mason and the other victim—Denson. That is a deep mystery indeed! And that horrible sign! Mr. Hewitt, you have done much—but not all!"

"No," replied Martin Hewitt, "not nearly all. It is even doubtful whether or not it will be my lot to come across the thing again; but it will be in the hands of the police. And, after all, we have achieved something. For we know that if Myatt can be captured we shall be at the heart of the mystery."