On the 25th she was certainly in London, and it is not very likely that she would go back to Edinburgh in order to dispose of the jewels there, where they could most easily be traced." "Not very likely, certainly," he assented drily.
"And," added the young girl, "on the day before she left for London, Lady Donaldson was alive." "And pray," he said suddenly, as with comic complacency he surveyed a beautiful knot he had just twisted up between his long fingers, "what has that fact got to do with it ?" "But it has everything to do with it!" she retorted.
"Ah, there you go," he sighed with comic emphasis.

"My teachings don't seem to have improved your powers of reasoning.

You are as bad as the police.

Lady Donaldson has been robbed and murdered, and you immediately argue that she was robbed and murdered by the same person." "But--" argued Polly.
"There is no but," he said, getting more and more excited.

"See how simple it is.