He paused and blew his nose on an unspeakable handkerchief. Wade slipped behind him and gave a spirited imitation of someone draining a glass to the dregs.

“You kept a list of the guests, I understand, and checked off the names as they came in.”

Mr. Singleton drew a piece of paper from his bosom and handed it to Alleyn with a slight bow.

“To witness if I lie,“ he explained grandly.

It was the list. Alleyn glanced at it and returned to the job.

“Did Mr. Ackroyd come out some time before the party?”

“Ackroyd, Ackroyd, Ackroyd. Let me see, let me see, let me see. Ackroyd. The comedian. Yes! Ackroyd came out.”

“You did not mention this to Mr. Wade.”

“I take my stand on that document!” said Mr. Singleton magnificently.

“Quite so. How long was Mr. Ackroyd away?”

“He returned in the twinkling of an eye.”

“You’re sure of that?”

“I am constant as the northern star,” said Mr. Singleton, stifling a slight hiccough. “Ackroyd eggzited and re-entered immediately. He went to the door of the office. He appeared to address those within. He returned.”

“You watched him?”

“With the very comment of my soul. Would it astonish you to learn that I played the Dane before—”

“Did you really? Mr. George Mason came out of the office some time before that, I believe?”

“George Mason, George! The manager. He did. I have already made a statement to this effect I believe, Mr. Wade?”

“That’s right, Joe, but Mr. Alleyn just wants to check up.”

Mr. Singleton inclined his head.

“Quite so. The manager, George Mason, came to the stage-door and repeated, gratuitously and unnesh — unessessraly, my instructions. I was to be sure to ask of each guest his local habitation and his name.”

“Mr. Mason returned to the office?”

“I swear it.”

“You may have to,” said Alleyn. “How long was Mr. Mason away from the office?”

“Let me see. Let me see. While one with moderate haste might tell an hundred. I showed him my list. I convinced him of my incorruptible purpose. I called to mind, I recollect, the coincidence that I had played the part of the porter in Macbeth, and of the sentry, Bernardo, in the Dane — that was in my green and salad days, Commissioner. I had scarce embarked on this trifling reminiscence when Mason turned up the collar of his dinner-jacket and observing that the air was chilly, turned and ran back to the office.”

Alleyn uttered a slight exclamation, glanced at Wade, and asked Singleton to repeat this statement, which he did at great length but to the same effect.

“Do you remember, now,” said Alleyn, “if the office door was open on to the yard as it is now?”

“It was open.”

“Ah yes. You know Dr. Te Pokiha by sight?”

“The native? Dark-visaged, like the Moor? The Moor was perhaps my greatest role. My favourite role. ‘Most potent grave—’

“Wonderful play, that,” interrupted Alleyn. “Dr. Te Pokiha was among the last guests to arrive, I think?”

“True.”

“Did you notice him coming?”

“I marked him come, yes. He too emerged from the office, carrying his mantle. He darted back and reappeared. He approached me and I admitted him, striking out his name as I did so.”

“Now, Mr. Singleton, I take it from what you have told me that you would be prepared to make a sworn statement that once Mr. Ackroyd, or Mr. Mason, or Dr. Te Pokiha had gone in at the stage-door they did not return to the office, and once they had gone to the office, did not return to the stage without your knowledge?”

“I have sworn it, indeed. In common parlance, sir, you can bet your boots and put your shirt on it”

“Well now, Mr. Singleton, I’m going to ask you to help me in a little experiment. Will you do this?”

“Impart! Proceed!”

“I want you to stand here by the stage-door and treat me as though I was Mr. Ackroyd, Dr. Te Pokiha, or Mr. Mason. As soon as I have gone, I want you to wait for five minutes and then walk along to the office. Will you do this?”

“Certainly.”

“Watch the office door,” said Alleyn, “and Mr. Wade will keep the time.” He glanced at Packer and Cass who had listened to the entire conversation with the liveliest interest. “You look steadily down the alley, you two. Are you keen on conjuring tricks?”

“I remember—” began Mr. Singleton; but Alleyn interrupted him.

“Will any gentleman in the audience provide me with a handkerchief? Sergeant Packer? Thank you. You are perfectly certain this is your handkerchief? You see me place it in the right-hand pocket of my jacket? I thank you. Now, Mr. Singleton, I am one of those three gentlemen aforesaid. You see me here in the yard. You are standing by the stage-door. I walk along the yard into the office. Got your watch out, Wade? Off we go.”

Singleton and the three officers stood in a group at the stage-door. Alleyn walked briskly down the yard and into the office, leaving the door open.

“What’s the idea, Mr. Wade?” asked Cass. “He’s a bit of a hard case, isn’t he?”

“He’ll do me,” said Packer. “He’s a corker.”

“Watch that door into the office,” snapped Wade. “And the yard.”

The door remained open on the yard. Nobody spoke. The sound of traffic in the street, and footsteps on the pavement outside, broke the silence. One or two people walked past at the end of the yard.

“He hasn’t come out, anyway,” said Cass.

“Time,” said Wade. “Come on, Singleton. Come on, you two.”

They all walked down the yard and into the office. Alleyn was sitting at the desk.

“Well!” said Alleyn brightly. “Still here, you see.”

“I thought, Superintendent,” said Mr. Singleton, “that you said we were to receive a surprise.”

“And you are disappointed?” He looked from one dubious face to the other. Wade was staring expectantly at him.

“I expect you’d like to know where the laugh and round of applause comes in,” said Alleyn. “If Sergeant Packer will look at the bottom rung of the back-stage ladder into the grid he will learn something to his advantage.”

“Go on, Packer,” said Wade.

Packer hurried off through the stage-door. There was a short pause and then he came thundering back.

“By cripey, Mr. Wade, it’s a corker! By gosh, Mr. Wade, it’s a humdinger!”

He was waving the handkerchief. Cass’s eyes opened very wide. Mr. Singleton moistened his lips once or twice but, for a marvel, he had nothing to say.

“Tied to the bottom rung it was,” declared Packer. “Tied to the bottom rung. By gum, it’s a beaut!”

“You see it can be done, Wade,” said Alleyn.

“It’s good enough,” said Wade delightedly, “it’s good enough.”

“Ah — um — very neat,” said Mr. Singleton. He drew the palm of his hand across his mouth. “I recollect seeing the Great Houdini—”

“Mr. Singleton,” said Alleyn, I’m afraid I’ve taken up far too much of your time. We mustn’t keep you any longer. Will you allow me to quote your favourite author? — ‘Spend this for me.’ ”

Mr. Singleton broke into a loud laugh as his fingers closed on the tip.

“Ah ha, sir, I can have at you again. ‘I’ll be your purse-bearer and leave you for an hour’.” He removed his hat, bowed, said “Good morning, gentlemen,” and hurried away.

“What a fabulous bit of wreckage,” said Alleyn. “Poor old devil, I wonder if he— Oh, well! I suppose you’d like an explanation of all this.” He turned to Cass and Packer.

“Too right, sir,“ said Packer. ”You’ve got us beat.”

“What I did was this. I came into this office, as you saw. I came out again as you apparently didn’t see, and I went round to the back by what I feel should be called Cass’s Alley.”

“But look here, sir, we were watching the yard.”

“I know. I left the door open and I sidled along to the street end keeping against the wall. I was hidden so far by the open door. If you go along to the stage-door you will see what I mean. I was just able to keep out of sight.”