“I know who uses black ones this shape,” said Harriet. “I once had the pleasure of sticking them in for her.”

“Miss de Vine, of course. Always the White Queen. And she would drop them all over the place. But I should think she was about the only person in College who would never, by any chance, come into this room. She gives no lectures or classes and never uses the dark-room or consults scientific works.”

“She was working in her room when I came across last night,” said Harriet.

“Did you see her?” said Wimsey, quickly.

“I’m sorry. I’m an idiot. I only meant that her reading-lamp was on, close to her window.”

“You can’t establish an alibi on the strength of a reading-lamp,” said Wimsey. “I’m afraid I shall have to do the floor-walk after all.”

It was the Dean who picked up a second hairpin-in the place where one might most reasonably expect to find it-in a corner near the sink in the dark-room. She was so pleased with herself as a detective that she almost forgot the implications of the discovery, till Harriet’s distressed exclamation forced them upon her.

“We haven’t identified the hairpins for certain,” said Peter, comfortingly. “That will be a little task for Miss Vane.” He gathered up the papers. “I’ll take these and add them to the dossier. I suppose there’s no message for us on the blackboard?”

He picked up the board, which contained only a few chemical formulae, scribbled in chalk, in Miss Edwards’s handwriting, and restored the easel to an upright position, on the far side of the window.

“Look!” said Harriet, suddenly. “I know why she went round that way. She meant to get out by the lecture-room window, and had forgotten the bars. It was only when she pulled the curtain aside and saw them that she remembered the dark-room and plunged away in a hurry, knocking over the blackboard and tumbling into the chairs on the way. She must have been between the window and the easel, because the board and the easel fell forward into the room, and not backwards towards the wall.”

Peter looked at her thoughtfully. Then he went back into the darkroom and lowered and raised the window-sash. It moved easily and almost in silence.

“If this place wasn’t so well built,” he said, almost accusingly, to the Dean, “somebody would have heard this window go up and run round in time to catch the lady. As it is, I wonder that Annie didn’t notice the noise of the beaker falling into the sink… But if she did, she probably thought it was something in the lecture-room-one of those glass cases or what not. You didn’t hear anything after you arrived, did you?”

“Not a thing.”

“Then she must have got out while Carrie was fetching you out of bed. I suppose nobody saw her go.”

“I’ve asked the only three students whose windows overlook that wall, and they saw nothing,” said Harriet.

“Well, you might ask Annie about the beaker. And ask both of them whether they noticed, as they came past, if the dark-room window was open or shut. I don’t suppose they noticed anything, but you never can tell.”

“What does it matter?” asked the Dean.

“Not very much. But if it was shut, it rather supports Miss Vane’s idea about the blackboard. If it was open, it would suggest that a retreat had been planned in that direction. It’s a question of whether we’re dealing with a short-sighted or a long-sighted person-mentally, I mean. And you might inquire at the same time whether any of the other women in the Scouts’ Wing saw the light in the lecture-room, and if so, how early.”

Harriet laughed.

“I can tell you that at once. None of them. If they had, there would have been an eager rush to tell us all about it. You may be perfectly certain that Annie’s and Carrie’s adventure formed the staple of conversation in the servants’ hall this morning.”

“That,” said his lordship, “is very true indeed.”

There was a pause. The lecture-room seemed to offer no further field for research. Harriet suggested that Wimsey might like to look round the College.

“I was about to suggest it,” said he, “if you can spare the time.”

“Miss Lydgate is expecting me in half an hour for a fresh attack on the Prosody,” said Harriet. “I mustn’t cut that, because her time is so precious, poor dear, and she’s suddenly thought of a new appendix.”

“Oh, no!” cried the Dean.

“Alas, yes! But we could just go round and view the more important battlefields.”

“I should like particularly to see the Hall and Library and the connection between them, the entrance to Tudor Building, with Miss Barton’s former room, the lay-out of the Chapel with reference to the postern and the place where, with the help of God, one leaps over the wall, and the way from Queen Elizabeth into the New Quad.”

“Great heavens!” said Harriet. “Did you sit up all night with the dossier?”

“Hush! no, I woke rather early. But don’t let Bunter hear, or he will start being solicitous. Men have died and the worms have eaten them, but not for early rising. In fact, it is said that it’s the early worm that gets the bird.”

“You remind me,” said the Dean, “that there are half-a-dozen worms waiting in my room to get the bird this minute. Three late-without-leaves two gramophones-out-of-hours, and an irregular motor-vehicle. We shall meet again at dinner, Lord Peter.”

She ran briskly away to deal with the malefactors, leaving Peter and Harriet to make their tour. From Peter’s comments, Harriet could make out little of his mind; she fancied, indeed, that he was somewhat abstracted from the matter in hand.

“I fancy,” he said at last, as they came to the Jowett Walk Lodge, where he had left the car, “that you will have very little more trouble at night.”

“Why?”

“Well, for one thing, the nights are getting very short, and the risks very great… All the same-shall you be offended if I ask you-if I suggest that you should take some personal precautions?”

“What sort of precautions?”

“I won’t offer you a revolver to take to bed with you. But I have an idea that from now on you and at least one other person may be in some danger of attack. That may be imagination. But if this joker is alarmed and bottled up for a bit-and I think she has been alarmed-the next outrage may be a serious one-when it comes.”

“Well,” said Harriet, “we have her word for it that she finds me merely funny.”

His attention seemed to be attracted by something among the dashboard fittings, and he said, looking not at her but at the car:

“Yes. But without any vanity, I wish I were your husband or your brother or your lover, or anything but what I am.”

“You mean, your being here is a danger-to me?”

“I dare say I’m flattering myself.”

“But it wouldn’t stop you to damage me.”

“She may not think very clearly about that.”

“Well, I don’t mind the risk, if it is one. And I don’t see why it would be any less if you were a relation of mine.”

“There’d be an innocent excuse for my presence, wouldn’t there?… Don’t think I’m trying to make capital out of this on my own account. I’m being careful to observe the formalities, as you may have noticed. I’m only warning you that I’m sometimes a dangerous person to know.”

“Let’s have this clear, Peter. You think that your being here may make this person desperate and that she may try to take it out of me. And you are trying to tell me, very delicately, that it might be safer if we camouflaged your interest in the case as another kind of interest.”

“Safer for you.”

“Yes-though I can’t see why you think so. But you’re sure I’d rather die than make such an embarrassing pretence.”

“Well, wouldn’t you?”

“And on the whole you’d rather see me dead than embarrassed.”

“That is probably another form of egotism. But I am entirely at your service.”

“Of course, if you’re such a perilous ally, I could tell you to go away.”