“So he ought to be — all took aback. When your best girl’s away ask a policeman. Sensible man, Felix Gardener, as well as a damn’ good actor. And I do love a crook play, I do.”

“Oh,” said Nigel, “I never thought of that. Rather a busman’s holiday for you, I’m afraid.”

“Not it. Is it the sort where you have to guess the murderer?”

“It is. And you’ll look a bit silly if you can’t, won’t you, inspector?”

“Shut up. I shall bribe this old gentleman to tell me. Here he comes.” Old Blair appeared at the end of the passage.

“Will you come this way, please?” he said, without returning to the door.

Nigel and Alleyn stepped inside the stage door of the Unicorn, and at that precise moment Chief Detective-Inspector Alleyn, all unknowingly, walked into one of the toughest jobs of his career.

They at once sensed the indescribable flavour of the working half of a theatre when the nightly show is coming on. The stage door opens into a little realm, strange or familiar, but always apart and shut in. The passage led directly on to the stage, which was dimly lit and smelt of dead scene paint, of fresh grease paint, of glue-size, and of dusty darkness, time out of mind the incense of the playhouse. A pack of scene flats leaned against the wall and a fireman leaned against the outer flat, which was painted to represent a section of a bookcase. A man in shirt sleeves and rubber-soled shoes ran distractedly round the back of the set. A boy carrying a bouquet of sweet peas disappeared into a brightly-lit entry on the right. The flats of the “set” vanished up into an opalescent haze. Beyond them, lit by shaded lamps, the furniture of a library mutely faced the reverse side of the curtain. From behind the curtain came the disturbing and profoundly exciting murmur of the audience, and the immemorial squall of tuning fiddle-strings. Through the prompt entrance another man in shirt sleeves stared into the flies.