“And quite obviously this wasn’t,” rejoined Mallett, tapping the letter with a broad forefinger. “I don’t pretend to be an expert in these matters, but at a guess I should say it was a light Hornington.”

He crumpled up the slips into a ball and threw them into the waste-paper basket with a shrug of disgust.

“And that’s that!” he observed. “Now where do we stand? Here we have a letter written on office-paper but not in the office—brought in from outside so that poor dear Gaveston could sign it. Who could get at the paper? Obviously, anyone employed in the office who cared to sneak a bit and take it home with him. Who owned a typewriter? Nowadays nearly everybody does. By the way, I wonder if Du Pine has one at his private house?”

“He certainly has,” said Frant, with an air of triumph. “Here’s a specimen of its work.”

He laid a sheet of notepaper before the inspector, adding: “It was addressed to the Chief Commissioner personally. It has just been sent down for us to deal with.”

My Lord,

Having applied several times in vain at my local police station, I am constrained to write to you personally and ask for police protection. As you may be aware, I was, until it ceased to carry on business, the secretary of the London and Imperial Estates Company Limited. Since giving evidence at the inquest on my late chairman, Mr. Ballantine, I have every reason to suppose that my life also is in danger. I have more than once observed some extremely suspicious characters prowling near my house. There is one on the pavement opposite to me as I write. I earnestly beg that my request, which in the circumstances I feel sure you will agree is no more than reasonable, may be attended to without delay.

I am, my lord.

Your obedient servant,

H. Du Pine.

Mallett placed the letter side by side with the other. “A different make of machine altogether,” he commented. “Just look at the tail of the ‘g’s’ for instance. Well, what do you suggest we do about this?”

“Take off our men, and put on uniformed constables,” said Frant promptly. “The suspicious characters were our own people, of course.”

Mallett pondered. “I think we can do better than that,” he replied after a pause. “Keep the same men on, but put them into uniform for the occasion. That will kill two birds with one stone. We shall be watching him then without his knowing it, and giving him what he wants at the same time.”

“I don’t quite see——” Frant began.