It was done by a thick pen, and these are fine.

No, it was done elsewhere, I should say.

Can you make anything of the inscription, Ames ?" "No, sir, nothing." "What do you think, Mr.Mac ?" "It gives me the impression of a secret society of some sort; the same with his badge upon the forearm." "That's my idea, too," said White Mason.
"Well, we can adopt it as a working hypothesis and then see how far our difficulties disappear.

An agent from such a society makes his way into the house, waits for Mr.Douglas, blows his head nearly off with this weapon, and escapes by wading the moat, after leaving a card beside the dead man, which will, when mentioned in the papers, tell other members of the society that vengeance has been done.

That all hangs together.
But why this gun, of all weapons ?" "Exactly." "And why the missing ring ?" "Quite so." "And why no arrest?
It's past two now.