It was in the room where Robert Turold had been murdered that Mr.Brimsdown questioned Thalassa about the letter, and heard with a feeling of dismay his declaration that he had not posted it.

Where was the nearest pillar box?
Nearly a mile away, at the cross-roads.

Could his late master have gone there to post it that night?
If he had, Thalassa hadn't heard him go out.

Could anybody else have posted it?
No; there was nobody else to post it.
It was like questioning a head on an old Roman coin, so expressionless was Thalassa's face as he delivered himself of these replies.

But the lawyer had the feeling that Thalassa was deriving a certain grim satisfaction from his questioner's perplexity, and he dismissed him somewhat angrily.
Then, when he had gone, he turned to an examination of some of the papers and documents which littered the room, but that was a search which told him nothing.
When the shades of evening warned him to relinquish that task, he told himself that he really ought to go and see Austin Turold before returning to Penzance.