“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.”

“But the entrance at the end! You had to cross there, and I swear I never took my eyes off it,” burst out Cass.

“You saw me walk across, Cass.”

“I never! Pardon me, sir.”

“You didn’t recognise your own overcoat and hat? You left them in here.”

Alleyn pointed to where they lay across the desk.

“I ventured to borrow them. As soon as I got in here I slipped them on, and, as I have said, sidled out under cover of the door, turned off to the right when I got out to the pavement, and then walked briskly back across the open end of the yard. You did not recognise me. Now, as soon as I got across the entrance to the yard I was hidden by the projecting bicycle shed. I repeated the sidling game on the other side and came back to Cass’s Alley. Once in there, I bolted round to the back door, having borrowed the key. All this took less than two minutes. Another half-minute going up the ladder. I allowed a minute to unhook the weight and came down in less than half. I put the key back in the door and returned by Cass’s Alley, reversing the process. I just had time to get your hat and coat off, before you came along. D’you see?”

“I don’t know that I do, sir, altogether,” confessed Cass, “but you did it, I reckon it’s right.”

“Come and look at the plan here, and you’ll see how it fits in.”

Wade, Packer, and Cass all stared solemnly at the plan.

“It’s a funny thing,” said Wade, “how easy it is to miss the obvious thing. That alleyway now. You’d have thought we’d have picked it for something straight away.”

“You’d have thought I would,” grunted Cass, “seeing I’m still sore from where I stuck.”