"About that typewriter," he said at once. "It's a rum thing. There's no doubt about it; the anonymous letter was written on the machine in the theatre. We tested that machine on the night of the affair, and found only Mr. Gardener's and Props's prints. Mr. Gardener used it in the play, so that was all right. Well, according to your instructions, sir, we've tested it again, and it's got no prints on the keyboard at all now, except on the letter Q, which still has Mr. Gardener's. I couldn't make it out at all, at first, but I reckon I've got an idea now."

"Yes? What is it, Bailey?"

"Well, sir—after we'd tested the machine it was put into the property-room. All the actors, as you know, were in the wardrobe-room. But Jacob Saint wasn't. He came in afterwards. Now, suppose he went into the property-room and rattled that off? The doors were shut. We wouldn't hear him on the stage, and it would only take a second or two. The paper was in the machine. He could put it in his pocket—you'd already searched him—and go off comfortably. The letter Q is out at the side, and he'd miss it when he wiped his prints off the keys."

"Where is the property-room?" asked Nigel.

"All down that passage to the stage door. It's a dock really. Big double doors open on to the stage, and, beyond old Blair's perch, there are other doors opening into the yard. See what I mean, sir? When Saint goes off with Miss Emerald he passes our man at the stage door, goes out into the yard, and slips into the dock by the pilot door that's cut in the big ones. The double doors on to the stage are shut. He turns on one light, types his letter, wipes over the keys, and slips out. And that dame knows what he's doing and keeps a look out."

"Still after the Emerald, I see," said Alleyn.

Nigel remembered his theory about Saint and the proscenium door. He advanced it modestly and was listened to by Detective Bailey with a kind of grudging respect peculiar to that official.

"Well," said Alleyn, "it's possible, Bailey. But any of the others could have done the typewriter business—or, at any rate, some of them could. Simpson could, for instance. Think a moment. Who was nearest to the stage door and most able to slip out unnoticed?"

Bailey stared at him.

"Gosh!" he said at last.

"You mean—old Blair?" Nigel said slowly.

"Who was asleep," added Alleyn placidly. The other two gaped at him.

"Well," said Alleyn, "nothing's conclusive, but everything is healthier. It all begins to come together very nicely."

"Glad you're pleased, sir," said Bailey with unexpected sarcasm.

"What about prints on the letter?"

"Only Mr. Gardener and Mr. Bathgate."

"And the paper from Surbonadier's flat? The one with the forged signature?"