"I'm afraid we've got to attach a great deal of importance to it," said Lord Peter gravely. "Now, what does Mary do? Either she thought the shot-"

"There was no shot."

"I know that. But I'm examining the discrepancies of her story. She said she did not give the alarm because she thought it was probably only poachers. But, if it was poachers, it would be absurd to go down and investigate. So she explains that she thought it might be burglars. Now how does she dress to go and look for burglars? What would you or I have done? I think we would have taken a dressing-gown, a stealthy kind of pair of slippers, and perhaps a poker or a stout stick-not a pair of walking shoes, a coat, and a cap, of all things!"

"It was a wet night," mumbled Parker.

"My dear chap, if it's burglars you're looking for you don't expect to go and hunt them round the garden. Your first thought is that they're getting into the house, and your idea is to slip down quietly and survey them from the staircase or behind the dining-room door. Anyhow, fancy a present-day girl, who rushes about bareheaded in all weathers, stopping to embellish herself in a cap for a burglar-hunt-damn it all, Charles, it won't wash, you know! And she walks straight off to the conservatory and comes upon the corpse, exactly as if she knew where to look for it beforehand."

Parker shook his head again.

"Well, now. She sees Gerald stooping over Cathcart's body. What does she say? Does she ask what's the matter? Does she ask who it is? She exclaims: 'God! Gerald, you've killed him,' and then she says, on second thoughts, 'Oh, it's Denis! What has happened? Has there been an accident?' Now does that strike you as natural?"

"No. But it rather suggests to me that it wasn't Cathcart she expected to see there, but somebody else."

"Does it? It rather sounds to me as if she was pretending not to know who it was. First she says, 'You've killed him!' and then, recollecting that she isn't supposed to know who 'he' is, she says, 'Why, it's Denis!'"

"In any case, then, if her first exclamation was genuine, she didn't expect to find the man dead."

"No-no-we must remember that. The death was a surprise. Very well. Then Gerald sends Mary up for help. And here's where a little bit of evidence comes in that you picked up and sent along. Do you remember what Mrs. Pettigrew-Robinson said to you in the train?"

"About the door slamming on the landing, do you mean?"

"Yes. Now I'll tell you something that happened to me the other morning. I was burstin' out of the bathroom in my usual breezy way when I caught myself a hell of a whack on that old chest on the landin', and the lid lifted up and shut down, plonk! That gave me an idea, and I thought I'd have a squint inside. I'd got the lid up and was lookin' at some sheets and stuff that were folded up at the bottom, when I heard a sort of gasp, and there was Mary, starin' at me, as white as a ghost. She gave me a turn, by Jove, but nothin' like the turn I'd given her. Well, she wouldn't say anything to me, and got hysterical, and I hauled her back to her room. But I'd seen something on those sheets."

"What?"

"Silver sand."

"Silver-"

"D'you remember those cacti in the greenhouse, and the place where somebody'd put a suit-case or something down?"

"Yes."

"Well, there was a lot of silver sand scattered about-the sort people stick round some kinds of bulbs and things."

"And that was inside the chest too?"

"Yes. Wait a moment. After the noise Mrs. Pettigrew-Robinson heard, Mary woke up Freddy and then the Pettigrew-Robinsons-and then what?"

"She locked herself into her room."

"Yes. And shortly afterwards she came down and joined the others in the conservatory, and it was at this point everybody remembered noticing that she was wearing a cap and coat and walking shoes over pyjamas and bare feet."

"You are suggesting," said Parker, "that Lady Mary was already awake and dressed at three o'clock, that she went out by the conservatory door with her suit-case, expecting to meet the-the murderer of her-damn it, Wimsey!"

"We needn't go so far as that," said Peter; "we decided that she didn't expect to find Cathcart dead."

"No. Well, she went, presumably to meet somebody."

"Shall we say, pro tem., she went to meet No. 10?" suggested Wimsey softly.

"I suppose we may as well say so. When she turned on the torch and saw the Duke stooping over Cathcart [garbled]-by Jove, Wimsey, I was right after all! When she said, 'You've killed him!' she meant No. 10-she thought it was No. 10's body."

"Of course!" cried Wimsey. "I'm a fool! Yes! Then she said, 'It's Denis-what has happened?' That's quite clear. And, meanwhile, what did she do with the suit-case?"

"I see it all now," cried Parker. "When she saw that the body wasn't the body of No. 10 she realised that No. 10 must be the murderer. So her game was to prevent anybody knowing that No. 10 had been there. So she shoved the suit-case behind the cacti. Then, when she went upstairs, she pulled it out again, and hid it in the oak chest on the landing. She couldn't take it to her room, of course, because if anybody'd heard her come upstairs it would seem odd that she should run to her room before calling the others. Then she knocked up Arbuthnot and the Pettigrew-Robinsons-she'd be in the dark, and they'd be flustered and wouldn't see exactly what she had on. Then she escaped from Mrs. P., ran into her room, took off the skirt in which she had knelt by Cathcart's side, and the rest of her clothes, and put on her pyjamas and the cap, which someone might have noticed, and the coat, which they must have noticed, and the shoes, which had probably left footmarks already. Then she could go down and show herself. Meantime she'd concocted the burglar story for the Coroner's benefit."

"That's about it," said Peter. "I suppose she was so desperately anxious to throw us off the scent of No. 10 that it never occurred to her that her story was going to help implicate her brother."

"She realised it at the inquest," said Parker eagerly. "Don't you remember how hastily she grasped at the suicide theory?"

"And when she found that she was simply saving-well, No. 10-in order to hang her brother, she lost her head, took to her bed, and refused to give any evidence at all. Seems to me there's an extra allowance of fools in my family," said Peter gloomily.

"Well what could she have done, poor girl?" asked Parker. He had been growing almost cheerful again. "Anyway, she's cleared-"

"After a fashion," said Peter, "but we're not out of the wood yet by a long way. Why is she hand-in-glove with No. 10, who is at least a blackmailer if not a murderer? How did Gerald's revolver come on the scene? And the green-eyed cat? How much did Mary know of that meeting between No. 10 and Denis Cathcart? And if she was seeing and meeting the man she might have put the revolver into his hands any time."

"No, no," said Parker. "Wimsey, don't think such ugly things as that."

"Hell!" cried Peter, exploding. "I'll have the truth of this beastly business if we all go to the gallows together!"

At this moment Bunter entered with a telegram addressed to Wimsey. Lord Peter read as follows:

"Party traced London; seen Marylebone Friday. Further information from Scotland Yard.-Police Superintendent Gosling, Ripley."

"Good egg!" cried Wimsey. "Now we're gettin' down to it. Stay here, there's a good man, in case anything turns up. I'll run round to the Yard now. They'll send you up dinner, and tell Bunter to give you a bottle of the Gateau Yquem-it's rather decent. So long." He leapt out of the flat, and a moment later his taxi buzzed away up Piccadilly.