Tommy and Tuppence were busy sorting correspondence. Tuppence gave an exclamation and handed a letter across to Tommy.

"A new client," she said importantly.

"Ha!" said Tommy. "What do we deduce from this letter, Watson? Nothing much, except the somewhat obvious fact that Mr.-er-Montgomery Jones is not one of the world's best spellers, thereby proving that he has been expensively educated."

"Montgomery Jones?" said Tuppence. "Now what do I know about a Montgomery Jones? Oh, yes, I have got it now. I think Janet St. Vincent mentioned him. His mother was Lady Aileen Montgomery, very crusty and high church, with gold crosses and things, and she married a man called Jones who is immensely rich."

"In fact the same old story," said Tommy. "Let me see, what time does this Mr. M. J. wish to see us? Ah, eleven thirty."

At eleven thirty precisely a very tall young man with an amiable and ingenuous countenance entered the outer office and addressed himself to Albert, the office boy.

"Look here-I say. Can I see Mr.-er-Blunt?"

"Have you an appointment, sir?" said Albert.

"I don't quite know. Yes, I suppose I have. What I mean is I wrote a letter-"

"What name, sir?"

"Mr. Montgomery Jones."

"I will take your name in to Mr. Blunt."

He returned after a brief interval.

"Will you wait a few minutes please, sir. Mr. Blunt is engaged on a very important conference at present."

"Oh-er-yes-certainly," said Mr. Montgomery Jones. Having, he hoped, impressed his client sufficiently Tommy rang the buzzer on his desk, and Mr. Montgomery Jones was ushered into the inner office by Albert.

Tommy rose to greet him, and shaking him warmly by the hand motioned towards the vacant chair.

"Now, Mr. Montgomery Jones," he said briskly, "what can we have the pleasure of doing for you?"

Mr. Montgomery Jones looked uncertainly at the third occupant of the office.

"My confidential secretary, Miss Robinson," said Tommy. "You can speak quite freely before her. I take it that this is some family matter of a delicate kind?"

"Well-not exactly," said Mr. Montgomery Jones.

"You surprise me," said Tommy. "You are not in trouble of any kind yourself, I hope?"

"Oh rather not," said Mr. Montgomery Jones.

"Well," said Tommy, "perhaps you will-er-state the facts plainly."

That, however, seemed to be the one thing that Mr. Montgomery Jones could not do.

"It's a dashed odd sort of thing I have got to ask you," he said hesitatingly. "I-er-I really don't know how to set about it."

"We never touch divorce cases," said Tommy.

"Oh Lord no," said Mr. Montgomery Jones. "I don't mean that. It is just, well-it's a deuced silly sort of a joke. That's all."

"Someone has played a practical joke on you of a mysterious nature?" suggested Tommy.

But Mr. Montgomery Jones once more shook his head.

"Well," said Tommy retiring gracefully from the position, "take your own time and let us have it in your own words."

There was a pause.

"You see," said Mr. Jones at last, "it was at dinner. I sat next to a girl."

"Yes?" said Tommy encouragingly.

"She was a-oh, well, I really can't describe her, but she was simply one of the most sporting girls I ever met. She's an Australian over here with another girl, sharing a flat with her in Clarges Street. She's simply game for anything. I absolutely can't tell you the effect that girl had on me."

"We can quite imagine it, Mr. Jones," said Tuppence.

She saw clearly that if Mr. Montgomery Jones' troubles were ever to be extracted a sympathetic feminine touch was needed, as distinct from the businesslike methods of Mr. Blunt.

"We can understand," said Tuppence encouragingly.

"Well, the whole thing came as an absolute shock to me," said Mr. Montgomery Jones, "that a girl could, well-knock you over like that. There had been another girl-in fact two other girls. One was awfully jolly and all that but I didn't much like her chin. She danced marvellously though and I have known her all my life which makes a fellow feel kind of safe, you know. And then there was one of the girls at the 'Frivolity.' Frightfully amusing, but of course there would be a lot of ructions with the mater over that, and anyway I really didn't want to marry either of them, but I was thinking about things you know and then-slap out of the blue-I sat next to this girl and-"

"The whole world was changed," said Tuppence in a feeling voice.

Tommy moved impatiently in his chair. He was by now somewhat bored by the recital of Mr. Montgomery Jones' love affairs.

"You put it awfully well," said Mr. Montgomery Jones. "That is absolutely what it was like. Only, you know, l fancy she didn't think much of me. You mayn't think it but I am not terribly clever."

"Oh, you mustn't be too modest," said Tuppence.

"Oh, I do realize that I am not much of a chap," said Mr. Jones with an engaging smile. "Not for a perfectly marvellous girl like that. That is why I just feel I have got to put this thing through. It's my only chance. She's such a sporting girl that she would never go back on her word."

"Well I am sure we wish you luck and all that," said Tuppence kindly. "But I don't exactly see what you want us to do."

"Oh Lordl" said Mr. Montgomery Jones. "Haven't I explained?"

"No," said Tommy. "You haven't."

"Well, it was like this. We were talking about detective stories. Una-that's her name-is just as keen about them as I am. We got talking about one in particular. It all hinges on an alibi. Then we got talking about alibis and faking them. Then I said-no, she said-now which of us was it that said it?"

"Never mind which of you it was," said Tuppence.

"I said it would be a jolly difficult thing to do. She disagreed-said it only wanted a bit of brain work. We got all hot and excited about it and in the end she said 'I will make you a sporting offer. What do you bet that I can produce an alibi that nobody can shake?"

"Anything you like, I said, and we settled it then and there. She was frightfully cocksure about the whole thing. 'It's an odds on chance for me,' she said. 'Don't be so sure of that,' I said. 'Supposing you lose and I ask you for anything I like?' She laughed and said she came of a gambling family and I could."

"Well?" said Tuppence as Mr. Jones came to a pause and looked at her appealingly.

"Well, don't you see? It is up to me. It is the only chance I have got of getting a girl like that to look at me. You have no idea how sporting she is. Last summer she was out in a boat and someone bet her she wouldn't jump overboard and swim ashore in her clothes, and she did it."

"It is a very curious proposition," said Tommy. "I am not quite sure I yet understand it."

"It is perfectly simple," said Mr. Montgomery Jones. "You must be doing this sort of thing all the time. Investigating fake alibis and seeing where they fall down."

"Oh-er-yes, of course," said Tommy. "We do a lot of that sort of work."

"Someone has got to do it for me," said Montgomery Jones. "I shouldn't be any good at that sort of thing myself. You have only got to catch her out and everything is all right. I daresay it seems rather a futile business to you but it means a lot to me and I am prepared to pay-er-all necessary whatnots you know."

"That will be all right," said Tuppence. "I am sure Mr. Blunt will take the case on for you."

"Certainly, certainly," said Tommy. "A most refreshing case, most refreshing indeed."

Mr. Montgomery Jones heaved a sigh of relief and pulled a mass of papers from his pocket and selected one of them. "Here it is," he said. She says, 'I am sending you proof I was in two distinct places at one and the same time. According to one story I dined at the Bon Temps Restaurant in Soho by myself, went to the Duke's Theatre and had supper with a friend, Mr. le Marchant, at the Savoy-but I was also staying at the Castle Hotel, Torquay, and only returned to London on the following morning. You have got to find out which of the two stories is the true one and how I managed the other."

"There," said Mr. Montgomery Jones. "Now you see what it is that I want you to do."

"A most refreshing little problem," said Tommy. "Very naive."

"Here is Una's photograph," said Mr. Montgomery Jones. "You will want that."

"What is the lady's full name?" inquired Tommy.

"Miss Una Drake. And her address is 180 Clarges Street."

"Thank you," said Tommy. "Well, we will look into the matter for you, Mr. Montgomery Jones. I hope we shall have good news for you very shortly."

"I say you know, I am no end grateful," said Mr. Jones rising to his feet and shaking Tommy by the hand. "It has taken an awful load off my mind."

Having seen his client out, Tommy returned to the inner office. Tuppence was at the cupboard that contained the Classic library.

"Inspector French," said Tuppence.

"Eh?" said Tommy.

"Inspector French of course," said Tuppence. "He always does alibis. I know the exact procedure. We have to go over everything and check it. At first it will seem all right and then when we examine it more closely we shall find the flaw."

"There ought not to be much difficulty about that," agreed Tommy. "I mean, knowing that one of them is a fake to start with makes the thing almost a certainty I should say. That is what worries me."

"I don't see anything to worry about in that."

"I am worrying about the girl," said Tommy. "She will probably be let in to marry that young man whether she wants to or not."

"Darling," said Tuppence, "don't be foolish. Women are never the wild gamblers they appear. Unless that girl was already perfectly prepared to marry that pleasant but rather empty-headed young man, she would never have let herself in for a wager of this kind. But, Tommy, believe me, she will marry him with more enthusiasm and respect if he wins the wager than if she has to make it easy for him some other way."