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.

“Don’t you? Well, just think it over for a bit. What is the job of a constable who is told off to give somebody or other house police protection? Obviously to watch any suspicious person who may appear outside the house, or who may approach somebody. But it isn’t to watch the behaviour of that somebody himself, is it? Nor is it part of his job to see what goes on in the house. There’s a very considerable difference. And I’ll tell you another thing, Frant. The average crook is apt to have a healthy respect for a plainclothes detective, but very little for the uniformed officer. He thinks of him as an ornament in the streets, just something to control traffic and arrest pickpockets, and so on. If Du Pine thinks he is being protected by ordinary flat-footed coppers he’ll be much more likely to give himself away than if he’s afraid he has a detective on his heels—that is if he has anything to give away.”

“Certainly he hasn’t done anything to give himself away yet,” Frant remarked.

“Perhaps he wasn’t quite satisfied in his mind about the ‘suspicious characters’,” said Mallett with a grin. “Now I’ve something else to tell you.”

He briefly told the sergeant of what he had seen on the dancing-floor of the Riviera Hotel.

“Odd, very odd,” said Frant, when he had done. “And the oddest part of it, if I may say so, is not that he should have been frightened at seeing you——”