Hetherwick went away from the sordid atmosphere of Fligwood's Rents wondering more than ever at this new development; he continued to wonder and to speculate all the rest of that day and most of the next. That Granett's sudden death had followed on Hannaford's seemed to him a sure proof that there was more behind this mystery than anybody had so far conceived of. Personally, he had not the slightest doubt that whoever poisoned Hannaford had also poisoned Granett. And he was not at all surprised when, late in the afternoon of the day following upon that of the visit to Dorking, Matherfield walked into his chambers with a face full of news.  
"I know what you're going to tell me, Matherfield," said Hetherwick, motioning his visitor to an easy chair. "The doctors have held a post-mortem on Granett, and they find that he was poisoned."
 
Matherfield's face fell; he was robbed of his chance of a dramatic announcement.
 
"Well, and that's just what I was going to tell you," he answered. "That's what they do say. Same doctors that performed the autopsy on Hannaford. Doesn't surprise you?"
 
"Not in the least," replied Hetherwick. "I expected it. They're sure of it?"
 
"Dead certain! But, as in Hannaford's case, they're not certain of the particular poison used. However—also as in his case—they've submitted the whole case to two big swells in that line, one of 'em the man that's always employed by the Home Office in these affairs, and the other that famous specialist at St. Martha's Hospital—I forget his name. They'll get to work; they're at work on the Hannaford case now. Difficult job, I understand—some very subtle poison, probably little known. However, I believe we've got a clue about it."
 
"A clue—about the poison?" exclaimed Hetherwick. "What clue?"
 
"Well, this," answered Matherfield. "After you'd gone away from Fligwood's Rents yesterday afternoon, and while I was making arrangements for the removal of the poor chap's body, I took another careful look round the room. Now, if you noticed things as closely as all that, you may have observed that Granett's bed was partly in a sort of alcove—the head part. In the corner of that alcove, or recess, just where he could have set them down by reaching his arm out of bed, I found a bottle and a glass tumbler. The bottle was an ordinary medicine bottle—not a very big one. It had the cork in it and about an inch of fluid, which, on taking out the cork, I found to be whisky, and, I should say by the smell, whisky of very good quality. But I noticed that there was the very slightest trace of some sort of sediment at the bottom. There was a trace of similar sediment in the bottom of the tumbler. Now, of course, I put these things up most carefully, sealed them, and handed them over to the doctors. For it was very evident to me—reconstructing things, you know—that Granett had mixed himself a drink, a nightcap, if you like to call it so, from that bottle on getting into bed, and then had put bottle and glass down by his bed-head, in the corner. And just as I mean to trace that five-pound note, Mr. Hetherwick, so I mean to trace that bottle!"
 
"How?" asked Hetherwick, closely interested. "And to what, or whom?"
 
"To the chemists where it came from," answered Matherfield. "It came from some chemist's, and I'll find which!"
 
"There are hundreds of chemists in London," said Hetherwick. "It's a stiff proposition."
 
"It's going to be done, anyway," asserted Matherfield. "And it mayn't be such a stiff job as it at first looks to be. See here! There were labels on that bottle, both of 'em torn and defaced, it's true, but still with enough on them to narrow down the field of inquiry. I've had the face of the bottle photographed—here's a print of the result."
 
He brought out a photographic print, roughly finished and mounted on a card, and handed it over to Hetherwick, who took it to the light and examined it carefully. It showed the front of the medicine bottle, with a label at the top and another at the bottom. Each had been torn, as if to obliterate names and addresses, but a good deal of the lettering was left.
 
 
    +-----------------------------+
    |    C. A     , Esq.,         |
    |    The mix  re as before    |
    |    No. A.1152               |
    +-----------------------------+
 
    +-----------------------------+
    |  _Note_.--This medicine has |
    |  been dispensed by a fully  |
    |  qualified Chemist with the |
    |          to possible drugs  |
    |              is guaranteed  |
    |                  wishes of  |
    |                  the Pres-  |
    |                             |
    |                  M.P.S.     |
    |                    St. W.C. |
    +-----------------------------+
 
"That bottom label's the thing, Mr. Hetherwick," remarked Matherfield. "Let me get that hiatus filled up with the name and address of the chemist, and I'll soon find out who C. A. blank, Esquire, is! The chemist is one in the West Central district; he's a member of the Pharmaceutical Society; he'll have somebody whose initials are C. A. on his books; he'll recognise the number A.1152 of the prescription. It's a decided clue; and even if there are, as there undoubtedly are, scores of chemists in the West Central district, I'll run this one down!"
 
Hetherwick handed back the photograph and began to pace up and down the room. Suddenly he turned on his visitor, his mind made up to tell him what he himself had been doing.
 
"Matherfield," he said, dropping into his chair again and adopting a tone of confidence, "what do you make of this? I mean—what's your theory? Is it your opinion that the deaths of these two men are—so to speak—all of a piece?"
 
"That is my opinion!" answered Matherfield with an emphatic nod. "I've no more doubt about it than I have that I see you, Mr. Hetherwick. All of a piece, to be sure! Whoever poisoned Hannaford poisoned Granett! I'll tell you how I've figured it out since the doctors told me, only a couple of hours since, what their opinion is about Granett. This way: Hannaford and Granett knew each other at Sellithwaite ten years ago. That night when Granett left Appleyard in Horseferry Road and turned into Victoria Street, he met Hannaford—accidentally."
 
"Why accidentally?" asked Hetherwick.
 
"Well, that's what I think," said Matherfield. "I've figured in that way. Of course, it may have been by appointment. But anyway, they met—we know that. Now then, where did they spend their time between then and the time they got into your carriage at St. James's Park? We don't know. But here comes in an unknown factor—what about the strange man at Victoria, the man muffled to his eyes? Two things suggest themselves to me, Mr. Hetherwick. Did Hannaford take Granett to see that man, or did Hannaford and Granett meet at that man's? For I think that ma............