Their prisoner was a stranger. He was a lean, furtive-looking man of thirty-five, below middle height, respectably dressed, and at first glance, the colonel, whose hobby was distinguishing at a look the social standing of humanity, was unable to place him.

Crewe locked the door.

"Now then," said the colonel, "what the devil were you doing listening at my door? Was that his game, Mr. Silva?"

"That was his game," said the other, brushing his hands.

"What have you got to say before I send for the police?" asked the colonel virtuously. "What have you got to say for yourself? Sneaking about a gentleman's flat, listening at keyholes!"

The man, who had been roughly handled, had risen and was putting his collar straight. If he had been taken aback by the sudden onslaught, he was completely self-possessed now.

"If you want to send for the police, you'd better start right away," he said; "you've got a telephone, haven't you? Perhaps I'll have a job for the policeman, too. You've no right to assault me, my friend," he said, addressing Pinto resentfully.

"What were you doing?" asked the colonel.

"Find out," said the man sharply.

The colonel stroked his long moustache, and his manner underwent a change.

"Now look here, old man," he said almost jovially; "we're all friends here, and we don't want any trouble. I daresay you've made a mistake, and my friend has made a mistake. Have a whisky and soda?"

The man grinned crooked.

"Not me, thank you," he said emphatically; "if I remember rightly, there was a young gentleman who took a glass of water in North Lambeth Police Court the other day, and----"

The colonel's eyes narrowed.

"Well, sit down and be sociable. If you're suggesting that I'm going to poison you, you're also suggesting that you know something which I don't want you to tell. Or that you have discovered one of those terrible secrets that the newspapers are all writing about. Now be a sensible man; have a drink."

The man hesitated.

"You have a drink of whisky out of the same bottle, and I'll join you."

"Help yourself," said the colonel good-naturedly. "Give me any glass you like."

The man went to the sideboard, poured out two pegs and sent the soda-water sizzling into the long glasses.

"Here's yours and here's mine," he said; "good luck!"

He drank the whisky off, after he had seen the colonel drink his, and wiped his mouth with a gaudy handkerchief.

"I'm taking it for granted," said the colonel, "that we've made no mistake and that you were listening at our door. Now we want no unpleasantness, and we'll talk about this matter as sensible human beings and man to man."

"That's the way to talk," said the other, smacking his lips.

"You've been sent here to watch me."

"I may have and I may not have," said the other.

Pinto shifted impatiently, but the colonel stopped him with a look.

"Now let me see what you are," mused the colonel, still wearing that benevolent smile of his. "You're not an ordinary tradesman. You've got a look of the book canvasser about you. I have it--you're a private detective!"

The man smirked.

"Perhaps I am," said he, "and," he added, "perhaps I'm not."

The colonel slapped him on the shoulder.

"Of course you are," he said confidently; "we don't see shrewd-looking fellows like you every day. You're a split!"

"Not official," said the man quickly.

He had all the English private detective's fear of posing as the genuine article.

"Now look here," said the colonel, "I'm going to be perfectly straight with you, and you've got to be straight with me. That's fair, isn't it?"

"Quite fair," said the man; "if I've been misconducting myself in any manner----"

"Don't mention it," said the colonel politely, "my friend here will apologise for handling you roughly, I'm sure; won't you, Mr. Silva?"

"Sure!" said the other, without any great heartiness.

He was tired of this conversation and was anxious to know where it was leading.

"You're not in the private detective business for your health," said the colonel, and the man shook his head.

"I bet you're working for a firm that's paying you about three pounds a week and your miserable expenses--a perfect dog's life."

"You're quite right there," said the man, and he spoke with the earnestness of the ill-used wage-earner,............