Hollis led the way farther along the alley, between high, black, windowless walls, and suddenly turning into a little court, paused before a door set deep in the side of an old half-timbered house.  
"Queer old place, this!" he remarked over his shoulder. "But you'll get a glass of as good port or sherry from this chap as you'd get anywhere in England—he knows his customers! Come in."
 
He led the way into a place the like of which Hetherwick had never seen—a snug, cosy room, panelled and raftered in old oak, with a bright fire burning in an open hearth and the flicker of its flames dancing on the old brass and pewter that ornamented the walls. There was a small bar-counter on one side of it; and behind this, in his shirt-sleeves, and with a cigar protruding from the corner of a pair of clean-shaven, humorous lips, stood a keen-eyed man, busily engaged in polishing wine-glasses.
 
"Good morning, gentlemen!" he said heartily. "Nice morning, Mr. Hollis, for the time o' year. And what can I do for you and your friend, sir?"
 
Hollis glanced round the room—empty, save for themselves. He drew a stool to the bar and motioned Hetherwick to follow his example.
 
"I think we'll try your very excellent dry sherry, Hudson," he answered. "That is, if it's as good as it was last time I tasted it."
 
"Always up to standard, Mr. Hollis, always up to standard, sir!" replied the bar-keeper. "No inferior qualities, no substitutes, and no trading on past reputation in this establishment, gentlemen! As good a glass of dry sherry here, sir, as you'd get where sherry wine comes from—and you can't say that of most places in England, I think. Everything's of the best here, Mr. Hollis—as you know!"
 
Hollis responded with a little light chaff; suddenly he bent across the bar.
 
"Hudson!" he said confidentially. "My friend here has something he'd like to show you. Now, then," he continued, as Hetherwick, in response to this, had produced the picture, "do you recognise that?"
 
The bar-keeper put on a pair of spectacles and turned the picture to the light, examining it closely. His lips tightened; then relaxed in a cynical smile.
 
"Aye!" he said, half carelessly. "It's the woman that did old Malladale out of that diamond necklace. Of course!—Mistress Whittingham!"
 
"Would you know her again, if you met her—now?" asked Hollis.
 
The bar-keeper picked up one of his glasses and began a vigorous polishing.
 
"Aye!" he answered, laconically. "And I should know her by something else than her face!"
 
Just then two men came in, and Hudson broke off to attend to their wants. But presently they carried their glasses away to a snug corner near the fire, and the bar-keeper once more turned to Hollis and Hetherwick.
 
"Aye!" he said confidentially. "If need were, I could tell that party by something else than her face, handsome as that is! I used to tell Hannaford when he was busy trying to find her that if he'd any difficulty about making certain, I could identify her if nobody else could! You see, I saw a deal of her when she was stopping at the 'White Bear.' And I knew something that nobody else knew."
 
"What is it?" asked Hetherwick.
 
Hudson leaned closer across the counter and lowered his voice.
 
"She was a big, handsome woman, this Mrs. Whittingham," he continued. "Very showy, dressy woman; fond of fine clothes and jewellery, and so on; sort of woman, you know, that would attract attention anywhere. And one of these women, too, that was evidently used to being waited on hand and foot—she took her money's worth out of the 'White Bear,' I can tell you! I did a deal for her, one way or another, and I'll say this for her: she was free enough with her money. If it so happened that she wanted things doing for her, she kept you fairly on the go till they were done, but she threw five-shilling pieces and half-crowns about as if they were farthings! She'd send you to take a sixpenny telegram and give you a couple of shillings for taking it. Well, now, as I say, I saw a deal of her, one way and another, getting cabs for her, and taking things up to her room, and doing this, that, and t'other. And it was with going up there one day sudden-like, with a telegram that had just come, that I found out something about her—something that, as I say, I could have told her by anywhere, even if she could have changed her face and put a wig on!"
 
"Aye—and what, now?" asked Hollis.
 
"This!" answered Hudson with a knowing look. "Maybe I'm a noticing sort of chap—anyhow, there was a thing I always noticed about Mrs. Whittingham. Wherever she was, and no matter how she was dressed, whether it was in her going-out things or her dinner finery, she always wore a band of black velvet round her right forearm, just above the wrist, where women wear bracelets. In fact, it was a sort of bracelet, a strip, as I say, of black velvet, happen about two inches wide, and on the front a cameo ornament, the size of a shilling, white stone or something of that sort, with one of these heathen figures carved on it. There were other folk about the place noticed that black velvet band, too—I tell you she was never seen without it; the chambermaids said she slept with it on. But on the occasion I'm telling you about, when I went up to her room with a telegram, I caught her without it. She opened her door to see who knocked—she was in a dressing-gown, going to change for dinner, I reckon, and she held out her right hand for what I'd brought her. The black velvet band wasn't on it, and for just a second like I saw what was on her arm!"
 
"Yes?" said Hollis. "Something—remarkable?"
 
"For a lady—aye!" replied Hudson, with a grim laugh. "Her arm was tattooed! Right round the place where she always wore this black velvet band there was a snake, red and green, and yellow, and blue, with its tail in its mouth!—wonderfully done, too; it had been no novice that had done that bit of work, I can tell you! Of course, I just saw it, and no more, but there was a strong electric light close by, and I did see it, and saw it plain and all. And that's a thing that that woman, whoever she may be, and wherever she's got to, can never rub off, nor scrub off!—she'll carry that to the day of her death."
 
The two listeners looked at each other.
 
"Odd!" remarked Hollis.
 
Hetherwick turned to the bar-keeper.
 
"Did she notice that you saw that her arm was tattooed?" he asked.
 
"Nay, I don't think she did," replied Hudson. "Of course, the thing was over in a second. I made no sign that I'd seen aught particular, and she said nought. But—I saw!"
 
Just then other customers came in, and the bar-keeper turned away to attend to their wants. Hollis and Hetherwick moved from the counter to one of the snug corners at the farther end of the room.
 
"Whoever she may be, wherever she may be—as Hudson said just now," remarked Hollis, "and if this woman really had anything to do with the mysterious circumstances of Hannaford's death, she ought not to be difficult to find. A woman who carries an indefaceable mark like that on her arm, and whose picture has recently appeared in a newspaper, should easily be traced."
 
"I think I shall get at her through the picture," agreed Hetherwick. "The newspaper production seems to have been done from a photograph which, from its clearness and finish, was probably taken by some first-class firm in London. I shall go round such firms as soon as I get back. It may be, of course, that she's nothing whatever to do with Hannaford's murder, but still, it's a trail that's got to be followed to the end now that one's started out on it. Well! that seems to finish my business here—as far as she's concerned. But there's another matter—I told you that when Hannaford came to town he had on him a sealed packet containing the secret of some invention or discovery, and that it's strangely and unaccountably missing. His granddaughter says that he worked this thing out—whatever it is—in a laboratory that he had in his garden. Now then, before I go I want to see that laboratory. As he's only recently left the place, I suppose things will still be pretty much as he left them at his old house. Where did he live?"
 
"He lived on the outskirts of the town," replied Hollis. "An old-fashioned house that he bought some years ago—I know it by sight well enough, though I've never been in it. I don't suppose it's let yet, though I know it's being advertised in the local papers. Let's get some lunch at the 'White Bear,' and then we'll drive up there and see what we can do. You want to get an idea of what it was that Hannaford had invented?"
 
"Just so," assented Hetherwick. "If the secret was worth all that he told his granddaughter it was, he may have been murdered by somebody who wanted to get sole possession of it. Anyway, it's another trail that's got to be worked on."
 
"I never heard of Hannaford as an inventor or experimenter," remarked Hollis. "But there, I knew little about him, except in his official capacity: he and his granddaughter, and an elderly woman they kept as a working housekeeper, were quiet sort of folk. I knew that he brought up his granddaughter from infancy, and gave her a rattling good education at the Girls' High School, but beyond that, I know little of their private affairs. I suppose he amused himself in this laboratory you speak of in his spare time?"
 
"Dabbled in chemistry, I understand," said Hetherwick. "And, if it hasn't been dismantled, we may find something in that laboratory that will give us a clue of some sort."
 
Hollis seemed to reflect for a minute or two.
 
"I've an idea!" he said suddenly. "There's a man who lunches at the 'White Bear' every day—a man named Collison; he's analytical chemist to a big firm of dyers in the town. I've seen him in conversation with Hannaford now and then. Perhaps he could tell us something on this point. Come on! this is just about his time for lunch."
 
A few minutes later, in the coffee-room of the hotel, Hollis led Hetherwick up to a bearded and spectacled man who had just sat down to lunch, and having introduced him, briefly detailed the object of his visit to Sellithwaite. Collison nodded and smiled.
 
"I understand," he said, as they seated themselves at his table. "Hannaford did dabble a bit in chemistry—in quite an amateur way. But as to inventing anything that was worth all that—come! Still, he was an ingenious man, for an amateur, and he may have hit on something fairly valuable."
 
"You've no idea what he was after?" suggested Hetherwick.
 
"Of late, no! But some time ago he was immensely interested in aniline dyes," replied Collison. "He used to talk to me about them. That's a subject of infinite importance in this district. Of course, as I dare say you know, the Germans have been vastly ahead of us as regards aniline dyes, and we've got most, if not all, of the stuff used, from Germany. Hannaford used to worry himself as to why we couldn't make our own aniline dyes, and I believe he experimented. But, with his resources, as an amateur, of course, that was hopeless."
 
"I've sometimes seen him talking to you," observed Hollis. "You've no idea what he was after, of late?"
 
"No. He used to ask me technical questions," answered Collison. "You know, I just regarded him as a man who had a natural taste for experimenting with things. This was evidently his hobby. I used to chaff him about it. Still, he was a purposeful man, and by reading and experiment he'd picked up a lot of knowledge."
 
"And, I suppose, it's within the bounds of possibility that he had hit on something of practical value?" suggested Hetherwick.
 
"Oh, quite within such bounds!—and he may have done," agreed Collison. "I've known of much greater amateurs suddenly discovering something. The question then is—do they know enough to turn their discovery to any practical purpose and account?"
 
"Evidently, from what he told his granddaughter, Hannaford did think he knew enough," said Hetherwick. "What I want to find out from a visit to his old laboratory is—what had he discovered?"
 
"And as you're not a chemist, nor even a dabbler," remarked Hollis, with a laugh, "that won't be easy! You'd better come with us after lunch, Collison."
 
"I can give you a couple of hours," assented Collison. "I'm already curious—especially if any discovery we can make tends to throw light on the mystery of Hannaford's death. Pity the police haven't got hold of the man who was with him," he added, glancing at Hetherwick. "I suppose you could identify him?"
 
"Unless he's an absolute adept at disguising himself, yes—positively!" replied Hetherwick. "He was a noticeable man."
 
An hour later the three men drove up to a house which stood a little way out of the town, on the edge of the moorland that stretched towards the great range of hills on the west. The house, an old-fashioned, solitary place, was empty, save for a caretaker who had been installed in its back rooms to keep it aired and to show it to possible tenants. The laboratory, a stone-walled, timber-roofed shed at the end of the garden, had never been opened, said the caretaker, since Mr. Hannaford locked it up and left it. But the key was speedily forthcoming, and the three visitors entered and looked round, each with different valuings of what he saw.
 
The whole place was a wilderness of litter and untidiness. Whatever Hannaford had possessed in the way of laboratory plant and appliances had been removed, and now there was little but rubbish—glass, whole and broken, paper, derelict boxes and crates, odds and ends of wreckage—to look at. But the analytical chemist glanced about him with a knowing eye, examining bottles and boxes, picking up a thing here and another there, and before long he turned to his companions with a laugh, pointing at the same time to a table in a corner which was covered with and dust-lined pots.
 
"It's very easy to see what Hannaford was after!" he said. "He's been trying to evolve a new ink!"
 
"Ink!" exclaimed Hollis incredulously. "Aren't there plenty of inks on the market?"
 
"No end!" agreed Collison with another laugh, and again pointing to the table. "These are specimens of all the better-known ones—British, of course, for no really decent ink is made elsewhere. But even the very best ink, up to now, isn't perfect. Hannaford perhaps thought, being an amateur, that he could make a better than the known best. Ink!—that's what he's been after. A superior, perfectly-fluid, penetrating, permanent, non-corrosive writing-ink—that's been his notion, a thousand to one! I observe the presence of lots of stuffs that he's used."
 
He showed them various things, explaining their properties and adding some remarks on the history of the manufacture of writing-inks during the last hundred years.
 
"Taking it altogether," he concluded, "and in spite of manufacturers' advertisements and boasting, there isn't a really absolutely perfect writing-fluid on the market—that I know of, anyway. If Hannaford thought he could make one, and succeeded, well, I'd be glad to have his formula! Money in it!"
 
"To the extent of a hundred thousand pounds?" asked Hetherwick, remembering what Rhona had told him. "All that?"
 
"Oh, well!" laughed Collison, "you must remember that inventors are always very sanguine; always apt to see everything through rose-coloured spectacles; invariably prone to exaggerate the merits of their inventions. But if Hannaford, by experiment, really hit on a first-class formula for making a writing-ink superior in all the necessary qualities to its rivals—yes, there'd be a pot of money in it. No doubt of that!"
 
"I suppose he'd have to take out a patent for his invention?" suggested Hetherwick.
 
"Oh, to be sure! I should think that was one of his reasons for going to London—to see after it." assented Collison. He looked round again, and again laughed. "Well," he said, "I think you know now—you may be confident about it from what I've seen here—what Hannaford was after! Ink—just ink!"
 
Hetherwick accepted this judgment, and when he left Sellithwaite later in the afternoon on his return journey to London, he summed up the results of his visit. They were two. First, he had discovered that the woman of whom Hannaford had spoken in the train was a person who ten years before had been known as Mrs. Whittingham, appeared to be some sort of an adventuress, and, in spite of her restitution to the jeweller whom she had defrauded, was still liable to arrest, conviction, and punishment—if she could be found. Second, he had found out that the precious invention of which Hannaford had spoken so confidently and enthusiastically to his granddaughter and the particulars of which had mysteriously disappeared, related to the manufacture of a new writing-ink, which might, in truth, prove a very valuable commercial asset. So far, so good; he was finding things out. As he ate his dinner in the restaurant car he considered his next steps. But it needed little consideration to resolve on them. He must find out all about the woman whose picture lay in his pocketbook—what she now called herself; where she was; how her photograph came to be reproduced in a newspaper; and, last, but far from least, if Hannaford, after seeing the reproduction, had got into touch with her or given information about her. To the man in the train Hannaford had remarked that he had said nothing about her until that evening—yes, but was that man the only man to whom he had spoken? So much for that—and the next thing was to find out somehow what had become of the sealed packet which Hannaford undoubtedly had on him when he went out of Malter's Hotel on the night of his death.