He woke, instantly and quietly, like a dog, the moment I approached him.

`Good night, Mr. Betteredge,' he said. `And mind, if you ever take to growing roses, the white moss rose is all the better for not being budded on the dog-rose, whatever the gardener may say to the contrary!'

`What are you doing here?' I asked. `Why are you not in your proper bed?'

`I am not in my proper bed,' answered the Sergeant, `because I am one of the many people in this miserable world who can't earn their money honestly and easily at the same time. There was a coincidence, this evening, between the period of Rosanna Spearman's return from the Sands and the period when Miss Verinder stated her resolution to leave the house. Whatever Rosanna may have hidden, it's clear to my mind that your young lady couldn't go away until she knew that it was hidden. The two must have communicated privately once already to-night. If they try to communicate again, when the house is quiet, I want to be in the way, and stop it. Don't blame me for upsetting your sleeping arrangements, Mr. Betteredge -- blame the Diamond.'

`I wish to God the Diamond had never found its way into this house!' I broke out.

Sergeant Cuff looked with a rueful face at the three chairs on which he had condemned himself to pass the night.

`So do I,' he said gravely.