rhona went back to her old quarters at the little hotel in surrey street for that night, and next morning hetherwick came round to her, with an armful of newspapers. finding her alone, he laid them on the table at her side with a significant nod of his head at certain big black letters which topped the uppermost columns.

"matherfield must have given plenty of informing news to the pressmen last night," he remarked with a grim smile. "it's all in there—his own adventures at southampton yesterday; mine and robmore's in westminster, and all the rest of it. i believe the newspaper people call this sort of thing a story—and a fine story it makes! winding up, of course, with the dramatic arrest of baseverie at waterloo! i'm afraid we're in for publicity for a time, worse luck!"

"shall we—shall i—have to appear at that man's trial?" asked rhona.

"that's unavoidable, i'm afraid, and at other things before that," answered hetherwick. "there'll be the proceedings before the magistrate, and the adjourned inquest, and so on. can't be helped; and there'll be some satisfaction in knowing that we're ridding the world of a peculiarly cruel and cold-blooded murderer! that chap baseverie is certainly as consummate a villain as i ever heard of. a human spider—and clever in his web-spinning. but i wish one had a few more particulars on one point—and yet i don't see how one's to get them."

"what point?" asked rhona.

"that sealed packet, containing the details, or formula, or whatever it is, of your grandfather's invention," replied hetherwick. "where is it? what, precisely, is it? did ambrose get it from him? has baseverie got it? so far as i can make out, the whole thing began with that. whether it was really worth a farthing or a fortune, your grandfather brought to london something which he honestly believed to be of great value, and there's no doubt that he got into the hands of those two men, ambrose and baseverie, because of it. there's no doubt, either, that in conversation with them, he told them, perhaps jokingly, what he knew about madame listorelle. nor is there any doubt that these two murdered him. nor is there any doubt, in my mind, as to how they murdered him! you must remember that both men were trained medical men, and, obviously of a scientific turn of mind into the bargain. each had doubtless made a deep study of poisons. such a knowledge is of value to such men as they were—men of criminal tendencies. probably they knew of a subtle poison easily administered, the effects of which would not be evident for some hours. no doubt they timed their work, so that their victim should die swiftly and suddenly when well away from their laboratory. and, of course, they did the same thing in the case of granett. granett paid the penalty of being with your grandfather. but for what did they murder your grandfather? did they get rid of him so that they could keep his secret about madame listorelle to themselves, and blackmail her and her sister, or that they could rob him of his invention and turn it to their own profit? if the latter, then——"

he paused, looking inquiringly at rhona, as if he expected her to see what he was after. but rhona shook her head.

"i don't follow," she said. "what then?"

"this," replied hetherwick. "if their desire to get hold of your grandfather's secret was their motive, then that secret's worth a lot of money! money which ought to come to you. don't you see? where is the secret? where's the sealed packet? i suppose the police would search baseverie last night—perhaps they found it on him. we shall hear—but, anyway it's yours."

rhona made a gesture of aversion.

"i should hate to touch or have anything to do with it if it had been in that man's possession!" she said. "but i don't think there's any doubt that they murdered my grandfather because of that secret. only, i think, too, they'd a double motive. the secret about madame listorelle was their second string. probably they believed that lady riversreade would be an easy prey. and i think she would have been, if she hadn't had major penteney to fall back on. i know she was dreadfully upset after baseverie's first visit. so i put it this way—always have done: they thought they could sell grandfather's invention for a lot of money, and get another lot out of lady riversreade and madame listorelle as blackmail."

"black money, indeed, all of it!" exclaimed hetherwick. "well——"

a woman-servant put her head into the little parlour in which they were sitting, and looked significantly at rhona.

"there's a policeman downstairs, miss, asking for you," she announced. "leastways, he wants to know if you can tell him if mr. hetherwick's here or been here."

hetherwick went to the head of the stair; a policeman standing in the hall below looked up and touched his helmet.

"inspector matherfield's compliments, sir, and could you step round and bring miss hannaford with you?" he asked. "there's new developments, mr. hetherwick. important!"

"we'll come at once," assented hetherwick. "ten minutes!" he went back and hurried rhona away. "what now?" he asked as they hastened towards matherfield's office. "perhaps they've extracted something out of baseverie? or possibly the newspapers have attracted the attention of somebody who can give further news?"

the last suggestion strengthened itself when, on entering matherfield's room, they found him closeted with two strangers whose appearance was that of responsible and well-to-do commercial men. all three were discovered in what looked like a serious and deep conversation, and hetherwick was quick to notice that the two unknown men looked at rhona with unusual interest. matherfield made haste to introduce her as the late ex-superintendent hannaford's granddaughter, and hetherwick as a gentleman who had been much concerned in the recent proceedings.

"these gentlemen, miss hannaford and mr. hetherwick," he proceeded, waving his hand at the others, "are messrs. culthwaite and houseover, manufacturing chemists, of east ham—incidentally, they've also a big place in lancashire. and having seen this morning's papers, in which, as you've no doubt noticed, there's a good deal about our affair, they've come straight to me with some news which will prove uncommonly useful when baseverie's put in the dock before the magistrate this afternoon. the fact is, mr. hetherwick, these gentlemen have supplied a missing link!"

"what link?" asked hetherwick eagerly.

matherfield nodded at the elder of the two men, culthwaite, who produced a pocket-book, and extracted from it a sheet of paper. silently, he passed it over to matherfield, who turned to rhona.

"now, miss hannaford," he said, with a note of triumph in his voice, "i dare say you can positively identify your grandfather's handwriting and his way of making figures? can you swear that this has been written by him?"

rhona gave but one glance at the paper before looking up with a glance of positive assertion.

"oh, yes!" she exclaimed. "that is his writing, without a doubt! nothing could be more certain!"

matherfield turned to hetherwick.

"that's the formula for the ink!" he said. "now we've got the big thing we wanted! and mr. culthwaite will tell you how he got it."

culthwaite, after allowing hetherwick to look at the paper, carefully replaced it in his pocket-book. there was an air of anxiety about him and about his partner concerning which hetherwick began to make guesses—they looked as if they were uncertain and uneasy. but culthwaite was ready enough to tell his story.

"we got it in this way," he said. "and i may as well say, as i've already said to you, mr. matherfield, that i don't think we should have got it at all if you police people hadn't been so reticent on that one particular point—if you'd noised it abroad about hannaford's secret we might have been forewarned. however, some little time ago, a man whom we knew as basing, and whom i firmly believe to be the baseverie that we've read about in the papers this morning—a man, mind you, that we'd done business with now and then during the last year or so—came to us and offered us the formula for a new black ink which he asserted would drive every known ink off the market, all over the world! he made extravagant claims for it; he swore it was the first absolutely perfect writing fluid ever invented. he brought a sample of it which he'd made up himself—he put it to various tests. but he did more—he offered us the use of the secret formula so that we ourselves could make and test it before deciding whether we'd fall in with his suggestion, which was that we should offer him a lump cash sum for the formula. well, we did make the ink, from the formula, and we did test it, and there is no doubt about it—it is all, and perhaps more, that basing, or baseverie claimed for its excellence. i needn't go into the drawbacks attaching to most well-known inks—this has none of them. and when basing came back to us, a few days ago, we decided to buy the formula from him. we agreed upon a cash price, and day before yesterday we paid the amount over—at our office in east ham."

"yes?" said hetherwick quietly. "and—what was the price agreed upon?"

the two partners exchanged a glance; it seemed to rhona, who was watching them intently, that they looked more uneasy than before. but culthwaite replied with promptitude.

"ten thousand pounds!"

"how did you pay him?" asked hetherwick. "in cash?"

"no—by open cheque, at his own request. that, of course, was as good as cash. but," continued culthwaite, "as soon as we read the newspapers this morning, we—that is, i, for i read the whole thing on my way to business—went at once to our bank to see if the cheque had been cashed. it had—an hour or two after we'd handed it to basing. he'd taken the amount in bank of england notes."

hetherwick looked at matherfield.

"of course," he remarked, as if he were asking a question, "that formula belongs to miss hannaford? baseverie had no right to sell it—he stole it?"

"that's the fact, mr. hetherwick," assented matherfield. "these gentlemen, innocently enough, bought stolen property. but i've just told them something that i'll now tell you. we found the money—notes—on baseverie, last night. intact—in his pocket-book. of course, with that, and the jewels which his accomplice succeeded in getting at southampton, he'd got a nice haul. but now we can easily prove how he came by that ten thousand—and it'll go back to messrs. culthwaite and houseover there. we can prove, too, from their evidence, that baseverie poisoned mr. hannaford for the sake of that formula. baseverie's done!"

"these gentlemen will recover their ten thousand pounds, then?" said hetherwick. "in that case"—he turned to the two partners—"i don't see that you've anything to worry about?" he suggested. "the formula, of course, must be handed over to——"

"well, now, that's just it, mr. hetherwick," interrupted the partner who until then had kept silent. "the fact is, sir, we don't want to lose that formula! we gave this man baring or baseverie ten thousand pounds for it, but——"

"but you really believe it to be worth more, eh?" said hetherwick with a smile. "i see! then in that case——"

"if we get back our ten thousand, sir, we shall be pleased to treat with the rightful owner," said culthwaite, after an exchange of looks with his partner. "in the meantime, the formula is safe and secret with us. we are well-known people——"

"we'll leave it at that, just now," answered hetherwick. "miss hannaford will trust you to keep your word about safety and secrecy. and later—business!" he got up, and rhona rose with him. "shall you want us to-day, matherfield?" he asked. "if not——"

"no!" replied matherfield. "merely formal business to-day—then, this afternoon, he'll be brought up. only evidence of arrest and application for adjournment. you can go away, mr. hetherwick—we'll let you both know when you're wanted."

hetherwick led rhona out, and once clear of the police precincts, smote his stick on the pavement.

"when we're through with this business i'm hanged if i ever dabble in crime affairs again, personally!" he exclaimed. "baseverie has been a pretty vile example to tackle! and that you should be dragged into it, too!" he added, suddenly. "that upset me more than anything. however, it's getting to an end, and then——"

he paused, while she looked up at him with a little wonder at his vehemence. then, and as they were at that moment walking along a quiet stretch of the less frequented side of the embankment, she timidly laid a hand on his arm. he turned sharply, laying his hand on hers.

"i think you've been very considerate and thoughtful for me," she said. "after all—it wasn't quite mere interest in crime that made you——"

"good lord, no!" he exclaimed quickly. "at first, perhaps, half that—half you! i felt—somehow—that i'd got to look after you. and then—and when you disappeared—but i believe i'm a bit muddle-headed! i'll tell you something—all that time you were lost, i—well, i scarcely ever slept! wondering, you know. and when you turned up yesterday afternoon—but i want to ask you something that i'm not quite clear about—i was certainly muddled just then!"

"what is it?" she asked.

hetherwick bent down to her and dropped his voice.

"i was so glad, so relieved to see you, yesterday afternoon," he said, "that—that i felt dazed—eh? and i want to know—did i kiss you?"

rhona suddenly looked up at him—and laughed.

"oh, really, how amusing you are!" she said. "why, of course, you did! twice!"

"that's good!" he exclaimed. "i—i thought perhaps i'd dreamt it. but—did you kiss me?"

"do you really want to be dead sure?" asked rhona mischievously. "very well—i did!"

"that's better!" said hetherwick.