But at once the other answered: "It's that big new building they've erected on the site of St. Andrews House. It fell in to the Crown on the death of the Duke of St. Andrews, and an American syndicate bought the site. Duke House, as they call it, was only opened last October. The lower storeys are big bachelor flats, and the top half of the building contains offices. Mr. Biddle, the American millionaire, has taken the first floor, but he hasn't settled in yet, and I don't think any of the offices have been let at all. They are asking very big rents, and they are justified, as it's one of the finest sites in the West End."

"I want you to get through to the porter of Duke House. Find out for me whether they have got an office let to a man—a Portuguese merchant I take him to be, of the name of Fernando Apra." He spelt out the name. "If you have any difficulty in getting the information, just go up there yourself in a taxi, and find out. But I'd like you to go back into your own rooms and try by telephone first."

There followed a long, painful ten minutes, during which Sir Angus, though as a rule he was a man of few words, tried to while away the time by explaining to the three people who were there why he thought it unlikely that the letter was genuine.

"You'd be amazed," he said, "to know the number of letters we receive purporting to contain important information which turn out to be false in every particular. There must be a whole breed of individuals who spend their time in writing annoying, futile letters, which, even if signed, are very seldom signed by the writer's real name. Some of those people are actuated by vulgar, stupid spite; others are hypnotised by the thought of a reward. And then, again, such letters are often written by people who have a grudge against the police, or, even more often, by some one who has a grudge against some ordinary person who has, maybe, done them a bad turn, or to whom they have done a bad turn! In the last few days we've had innumerable letters, from all over the kingdom, concerning Mr. Pavely's disappearance. It is just possible that this man"—he looked down again at the sheet of typewritten paper—"has an office in Duke House, but I think it very unlikely that Mr. Godfrey Pavely was even acquainted with him——"

The door opened.

"Yes, sir, the party in question has got an office there right enough, but he hasn't been at Duke House for some time—some three weeks, the porter said. He took the office late in October, and for a time he was there, on and off, a good deal. The porter don't quite know what his business is, but as far as he knows he gives him a good character. His office is right at the very top of the house, the only one let on that floor."

An unpleasant little trickle of doubt came over Sir Angus's mind. When he had first read the typewritten letter, he had doubted very much if there was such a building in existence as Duke House, Piccadilly. Then, after he had heard that the place was there, after, as a matter of fact, it had been recalled to his memory by his subordinate, he had fallen back on the belief that there would be no person of the name of Fernando Apra to be found in Duke House.

He now fell back on a third position. Doubtless this extraordinary letter had been written by some enemy of the man Apra who wished to cause him the unpleasantness of a visit from the police.

After a few moments' thought Sir Angus Kinross proposed something which none of the three people there knew to be a most surprising departure from his usual rule.

"What would you say, Lord St. Amant, if you and I were to go up there now, to Duke House—accompanied, of course, by two of my men? That, at any rate, would put an end to Mrs. Pavely's suspense. If she doesn't mind doing so, Mrs. Pavely and her friend can wait here, in my private room."