"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.