This was quite easy to say, but to eat under the circumstances was too much for either of the young householders.  The luncheon left the table practically untouched; and when it was over Thaddeus called his man into the house, wrote a note to the police-station, asking for an officer in citizen’s clothes at once, and despatched it by him, with the injunction to let very little grass grow under his feet on the way down to headquarters.  He then summoned the waitress into the library.

“Have you said anything to Margaret about the china?” he asked.

“Yes, sir,” she replied.

“What did you say?”

“I told her as how wasn’t it funny the way it had went, sir.”

“And what did she say?”

“Nothing, sir.  Only she seemed to think it was funny, because she laughed.”

“And what did you say then?”

“Nothing, Mr. Perkins.  Margaret and me have very little conversation, because she don’t fancy me, and prefers talkin’ to herself like.”

“H’m!” said Thaddeus.  “Talks to herself, does she?”

“All the time, sir,” returned the waitress, “and she seems very fond of it, sir.  She laughs, and says things, and then laughs again.  She does it by the hour.”

“How long has this been going on?”

“About a week, sir.  I noticed it first last time I had my day out.  I didn’t get in until nearly eleven o’clock, and I found her sitting at the table havin’ supper and talkin’ and laughin’ like as though there was folks around.”

“She was entirely alone, was she?” asked Thaddeus.

“Yes, sir.”

“What did you do when you came in?”

“I said ‘Hello’ to her and sat down opposite to her at the table, where there was a place set, and I told her I was glad she had something to eat and a place set for me, because I hadn’t had any supper and I was hungry, sir.”

“Did she make any reply?”

“No, sir.  She looked at me kind of indignant, and turned out the gas and went up to bed, leaving me in the dark.”

Thaddeus’s brow grew thoughtful again.  It wrinkled into a half-dozen lines as he asked: 

“Why didn’t you speak of this before?”

“It ain’t for me to be telling tales, Mr. Perkins,” she said.  “All cooks as I’ve lived with is queer like, and I didn’t think any more about it.”

“All right,” said Thaddeus.  “You may go.  Only, Mary, don’t speak of the plates again to Margaret.  Say as little to her as you can, in fact, about anything.  If you notice anything queer, report to me at once.”

The waitress left the room, and Thaddeus turned to his desk.  It was plain from his appearance that light was beginning to be let in on places that up to this point had been more or less dark to him, although, as a matter of fact, he could not in any way account for the mystery of the vanished plates any more than he could for the sweeping of the library in the still hours of the night.  He had an idea as to who the culprit was, and what that idea was is plain enough to us, but the question of motive was the great puzzle to him now.