“I’m banking on the fact that an anonymous letter writer can’t stop writing letters. She may know it’s dangerous, but she’ll have to do it. It’s like a craving for drink or drugs.”

I nodded.

“Now you see, Mr. Burton, I fancy whoever it is will want to keep the letters looking the same as much as possible. She’s got the cut-out pages of that book, and can go on using letters and words cut out of them. But the envelopes present a difficulty. She’ll want to type them on the same machine. She can’t risk using another typewriter or her own handwriting.”

“Do you really think she’ll go on with the game?” I asked incredulously.

“Yes, I do. And I’ll bet you anything you like she’s full of confidence. They’re always vain as hell, these people! Well, then, I figured out that whoever it was would come to the Institute after dark so as to get at the typewriter.”

“Miss Ginch,” I said.

“Maybe.”

“You don’t know yet?”

“I don’t know.”

“But you suspect?”

“Yes. But somebody’s very cunning, Mr. Burton. Somebody knows all the tricks of the game.”

I could imagine some of the network that Nash had spread abroad. I had no doubt that every letter written by a suspect and posted or left by hand was immediately inspected. Sooner or later the criminal would slip up, would grow careless.

For the third time I apologized for my zealous and unwanted presence.

“Oh well,” said Nash philosophically. “It can’t be helped. Better luck next time.”

I went out into the night. A dim figure was standing beside my car. To my astonishment I recognized Megan.

“Hallo!” she said. “I thought this was your car. What have you been doing?”

“What are you doing is much more to the point?” I said.

“I’m out for a walk. I like walking at night. Nobody stops you and says silly things, and I like the stars, and things smell better, and everyday things look all mysterious.”

“All of that I grant you freely,” I said. “But only cats and witches walk in the dark. They’ll wonder about you at home.”

“No, they won’t. They never wonder where I am or what I’m doing.”

“How are you getting on?” I asked.

“All right, I suppose.”

“Miss Holland look after you and all that?”

“Elsie’s all right. She can’t help being a perfect fool.”

“Unkind—but probably true,” I said. “Hop in and I’ll drive you home.”

It was not quite true that Megan was never missed.

Symmington was standing on the doorstep as we drove up.

He peered towards us. “Hallo, is Megan there?”

“Yes,” I said. “I’ve brought her home.”

Symmington said sharply:

“You mustn’t go off like this without telling us, Megan. Miss Holland has been quite worried about you.”