He found that he had made up his mind that Saint was responsible for the murder. Yet Saint's was the best of all the alibis. He had been alone in the audience, but Blair had sworn positively that he had not seen the proprietor of the Unicorn return to the stage between the acts. Saint had been in a box, and it was just possible that he could have slipped out during the black-out. At this point Nigel got his brain-wave. Suppose Jacob Saint had left his box under cover of the black-out and had gone through the door in the proscenium, on to the stage. This door had been locked when Stavely and Nigel went through, but Saint might easily have got hold of a key. There he would be, before the lights went out, in his box facing the audience, as large as life. Then complete darkness. Saint had left the box, slipped through the door, which he had perhaps previously unlocked, gone straight to the desk, colliding with Gardener on the way, pulled out the drawers and replaced the dummies with the cartridges. When the lights went up again—there was Mr. Saint sitting in his box at the Unicorn. Nigel was thrilled with himself and rang up Scotland Yard. Alleyn was out, but had made an appointment for four o'clock. Nigel said he would be there at 4.30.

He felt fidgety and unable to settle down to anything. He was big with his theory. Presently he thought of Felix Gardener, and decided to walk round to Sloane Street and talk it over with him. He didn't ring up. If Felix was out he would walk on down to Knightsbridge and take a bus to the Yard. He wanted exercise.

Sloane Square, that full stop between Eatonia and Chelsea, had a look of sunny friendliness. Nigel bought a carnation for his coat, sent a silly telegram to his Angela, and walked lightly onwards. Sloane Street, with its air of quality and hint of boredom, was busier than usual. Nigel felt a sudden inclination to run, to whistle, to twirl his stick round. He glanced jauntily at a shabby-genteel man, who stood looking into the furniture shop next the flat. Gardener's windows on the first floor were open. He spoke blithely to the commissionaire, refused the lift, and ran two steps at a time up the thickly-carpeted stairs to Gardener's door.

It was open and Nigel, without ringing, went into the little entrance hall that opened into the studio sitting-room. He was about to call out, cheerfully, and had actually drawn in his breath to do so, when he was brought up short by a woman's voice coming from the studio room.

"If I did it," it cried urgently, "it was for you—for you, Felix. He was your worst enemy."

Nigel heard Gardener say slowly: "I can't believe it. I can't believe it."

The woman began to laugh.