“Quite,” said Alleyn. Fabian suddenly offered him a cigar which he refused.

“Well, as I say, she was very helpful in many ways but she did gimlet rather and she used to talk jolly indiscreetly at meal times.”

“You should have heard her,” said Fabian. “ ‘Now what do my two inventors think?’ And then, you know, she’d pull an arch face and, for all the world like one of the weird sisters in Macbeth, she’d lay her rather choppy finger on her lips and say: ‘But we mustn’t be indiscreet, must we?’ ”

Alleyn glanced up at the picture. The spare, wiry woman stared down at him with the blank inscrutability of all Academy portraits. He was visited by a strange notion. If the painted finger should be raised to those lips that seemed to be strained with such difficulty over projecting teeth! If she could give him a secret signal: “Speak now. Ask this question. Be silent here, they are approaching a matter of importance.”

“That’s how she carried on,” Douglas agreed. “It was damned difficult and of course everybody in the house knew we were doing something hush-hush. Fabian always said: ‘What of it? We keep our stuff locked up and even if we didn’t nobody could understand it.’ But I didn’t like the way Flossie talked. Later on her attitude changed.”

“That was after questions had been asked in the House about leakage of information to the enemy,” said Ursula. “She took that very much to heart, Douglas, you know she did. And then that ship was torpedoed off the North Island. She was terribly upset.”

“Personally,” said Fabian, “I found her caution much more alarming than her curiosity. You’d have thought we had the Secret Death Key of fiction on the stocks. She papered the walls with cautionary posters. Go on, Douglas.”

“It was twenty-one days before she was killed that it happened,” said Douglas. “And if you don’t find a parallel between my experience and Ursy’s, I shall be very much surprised. Fabian and I had worked late on a certain improvement to a crucial part of our gadget — a safety device, let us call it.”

“Why not,” said Fabian, “since it is one?”

“I absolutely fail to understand your attitude, Fabian, and I’m sure Mr. Alleyn does. Your bloody English facetiousness—”

“All right. You’re perfectly right, old thing, only it’s just that all these portentous hints seem to me to be so many touches. You know as well as I do that the idea of a sort of aerial magnetic mine must have occurred to countless schoolboys. The only thing that could possibly be of use to the most sanguine dirty dog would be either the drawings, or the dummy model.”

“Exactly!” Douglas shouted and then immediately lowered his voice. “The drawings and the model.”

“And it’s all right about Markins. He’s spending the evening with the Johns family.”

“So he says,” Douglas retorted. “Well now, sir, on this night, a fortnight before Aunt Floss was killed, I was worrying about the alteration in the safety device—”

His story did bear a curious resemblance to Ursula’s.

On this particular evening, at about nine o’clock, Douglas and Fabian had stood outside their workroom door, having locked it for the night. They were excited by the proposed alteration to the safety device which Fabian now thought could be improved still further. “We’d talked ourselves silly and decided to chuck it up for the night,” said Douglas. He usually kept the keys of the workroom door and safe, but on this occasion each of them said that he might feel inclined to return to the calculations later on that night. It was agreed that Douglas should leave the keys in a box on his dressing-table where Fabian, if he so desired, could get them without disturbing him. It was at this point that they noticed Markins, who had come quietly along the passage from the backstairs. He asked them if they knew where Mrs. Rubrick was as a long-distance call had come through for her. He almost certainly overheard the arrangement about the keys. “And, by God,” said Douglas, “he tried to make use of it.”

They parted company and Douglas went to bed. But he was over-stimulated and slept restlessly. At last, finding himself broad awake and obsessed with their experiment, he had decided to get up and look through the calculations they had been working on that evening. He had stretched out his hand to his bedside table when he heard a sound in the passage beyond his door. It was no more than the impression of stealthy pressure, as though someone advanced with exaggerated caution and in slow motion. Douglas listened spell-bound, his hand still outstretched. The steps paused outside his door. At that moment he made some involuntary movement of his hand and knocked his candlestick to the floor. The noise seemed to him to be shocking. It was followed by a series of creaks fading in a rapid diminuendo down the passage. He leapt out of bed and pulled open his door.

The passage was almost pitch-dark. At the far end it met a shorter passage that ran across it like the head of a T. Here, there was a faint glow that faded while Douglas watched it as if, he said, somebody with a torch was moving away to the left. The only inhabited room to the left was Markins’. The backstairs were to the right.

At this point in his narrative, Douglas tipped himself back on the sofa and glanced complacently about him. Why, he demanded, was Markins abroad in the passage at a quarter to three in the morning (Douglas had noted the time) unless it was upon some exceedingly dubious errand? And why did he pause outside his, Douglas’, door? There was one explanation which, in the light of subsequent events, could scarcely be refuted. Markins had intended to enter Douglas’ room and attempt to steal the keys to the workshop.

“Well, well,” said Fabian, “let’s have the subsequent events.”

They were, Alleyn thought, at least suggestive.

After the incident of the night Douglas had taken his keys to bed with him and lay fuming until daylight, when he woke Fabian and told him of his suspicions. Fabian was sceptical. “A purely gastronomic episode, I bet you anything you like.” But he agreed that they should be more careful with the keys, and he himself contrived a heavy shutter which padlocked over the window when the room was not in use. “There was no satisfying Douglas,” Fabian said plaintively. “He jeered at my lovely shutter and didn’t believe I went to bed with the keys on a bootlace round my neck. I did though.”

“I wasn’t satisfied to let it go like that,” said Douglas. “I was damned worried and next day I kept the tag on Master Markins. Once or twice I caught him watching me with a very funny look in his eye. That was on the Thursday. Flossie had given him the Saturday off and he went down to the Pass with the mail car. He’s friendly with the pub keeper there. I thought things over and decided to do a little investigation, and I think you’ll agree I was justified, sir. I went to his room. It was locked, but I’d seen a bunch of old keys hanging up in the store-room and after filing one of them I got it to function all right.” Douglas paused, half-smiling. His arm still rested along the back of the sofa behind Terence Lynne. She turned and, clicking her knitting needles, looked thoughtfully at him.

“I don’t know how you could, Douglas,” said Ursula. “Honestly!”

“My dear child, I had every reason to believe I was up against a very nasty bit of work — a spy, an enemy. Don’t you understand?”

“Of course I understand, but I just don’t believe Markins is a spy. I rather like him.”

Douglas raised his eyebrows and addressed himself pointedly to Alleyn.

“At first I thought I’d drawn a blank. Every blinking box and case in his room, and there were five all told, was locked. I looked in the cupboard and there, on the floor, I did discover something.”

Douglas cleared his throat, took a wallet from his breast pocket and an envelope from the wallet. This he handed to Alleyn. “Take a look at it, sir. It’s not the original. I handed that over to the police. But it’s an exact replica.”