"Because Granett knew that Ambrose lived in John Street, close by," replied Mapperley with promptitude. "He may have known it before; he may not have known it until that evening. But—he knew it! Most likely he thought that Ambrose had returned home from the place in Westminster: Ambrose may have left there before Hannaford and Granett did. Anyway, we may be reasonably certain that when Granett left you with the dying or dead man, he ran off to Ambrose's flat—a few minutes away."
"Why didn't he come back?" demanded Hetherwick. "I'm only wanting to get at probabilities."
"I've thought of that, too," replied Mapperley. "I think he found Ambrose out. But by that time he'd had time to reflect. He knew something was wrong. He knew that if he went back, he'd find the police there, and would be questioned. He might be suspected. And so—he went home, with the bottle in which Ambrose had given him a drop of whisky for himself. And—died in his sleep, as they thought Hannaford would."
"Why should Ambrose have that bottle down at Westminster?" asked Hetherwick.
"Why shouldn't he?" retorted Mapperley. "A man who's taking a tonic takes it at least three times a day—regularly. He'd have his bottle with him. Probably there are several similar empty bottles there at that place."
"Where is that place?" exclaimed Hetherwick. "Where?"
"Got to be found," said Mapperley, as the cab came to a stand. "But—here's this!"
Hetherwick led his companion across Paddington Green and to the house from which he and Matherfield had watched the flats opposite. Late as it was, the lodging-house keeper was up, and lent a willing ear to Hetherwick's request that he should go with him to his friend the caretaker of the Mansions. That functionary was at supper. He continued to sup as Hetherwick, morally supported by the lodging-house man, explained matters to him, but at last he allowed his cheek to bulge with unswallowed food and turned a surprised and knowing eye on his principal visitor.
"Blamed if I didn't wonder whether it was all O.K. with that chap!" he exclaimed, banging the table with the haft of his knife. "For all he was quite the gentleman, I somehow suspicioned him! And yet, he'd a straight tale to tell: come here on Madame's behalf, to get something for her out of her rooms, had her keys, and give me a note from her saying as how I was to allow the bearer to go up to her flat! What more could I expect—and what could I do—under the circs? I asks yer!"
"Oh, he had a note, had he?" inquired Hetherwick. "In Madame's writing?"