"They couldn't. There was no one about."

"There is a balcony outside the window. Somebody might have been there, peeping in. Or, who knows, someone might have been looking through the keyhole."

"You've got keyholes on the brain, Poirot. People don't really spend their time looking through keyholes as much as you seem to think." Poirot half closed his eyes and remarked that I had always had too trusting a nature.

"And let me tell you, very funny things happen with keys in this house. Me, I like to feel that my door is locked on the inside, even if the good Curtiss is in the adjoining room. Soon after I am here, my key disappears - but entirely! I have to have another one made."

"Well, anyway," I said with a deep breath of relief, my mind still laden up with my own troubles, "it didn't come off. It's awful to think one can get worked up like that." I lowered my voice. "Poirot, you don't think that because - because of that murder long ago there's a sort of infection in the air?"

"A virus of murder, you mean? Well, it is an interesting suggestion."

"Houses do have an atmosphere," I said thoughtfully. "This house has a bad history."

Poirot nodded.

"Yes. There have been people here - several of them - who desired deeply that someone else should die. That ls true enough."

"I believe it gets hold of one in some way. But now, Poirot, tell me, what am I to do about all this - Judith and Allerton, I mean? It's got to be stopped somehow. What do you think I'd better do?"

"Do nothing," said Poirot with emphasis.

"Oh, but - "

"Believe me, you will do least harm by not interfering."

"If I were to tackle Allerton - "

"What can you say or do? Judith is twenty-one and her own mistress."

"But I feel I ought to be able - "

Poirot interrupted me.

"No, Hastings. Do not imagine that you are clever enough, forceful enough, or even cunning enough to impose your personality on either of those two people. Allerton is accustomed to dealing with angry and impotent fathers, and probably enjoys it as a good joke. Judith is not the sort of creature who can be browbeaten. I would advise you - if I advised you at all - to do something very different. I would trust her, if I were you."

I stared at him.

"Judith," said Hercule Poirot, "is made of very fine stuff. I admire her very much." I said, my voice unsteady:

"I admire her, too. But I'm afraid for her."

Poirot nodded his head with sudden energy.

"I, too, am afraid for her," he said. "But not in the way you are. I am terribly afraid. And I am powerless - or nearly so. And the days go by. There is danger, Hastings, and it is very close."

II

I knew as well as Poirot that the danger was very close. I had more reason to know it than he had, because of what I had actually overheard the previous night. Nevertheless I pondered on that phrase of Poirot's as I went down to breakfast. "I would trust her if I were you."