Every accessible door and window on the basement and first floor was examined, and, with the exception of the piazza door, which Thaddeus remembered to have unlocked himself a few minutes before, every lock was fastened.  The disturbance had come from within.

“And Bess must never know it,” said he; “it would worry her to death.”  And then came a thought to Thaddeus’s mind that almost stopped the beating of his heart.  “Unless she has discovered it in my absence,” he gasped.  In an instant he was mounting the stairs to hasten to Bessie’s side, as though some terrible thing were pursuing him.

“Well, what was it, Ted?” she asked, as he entered the room.

Perkins gave a sigh of relief.  All was safe enough above-stairs at least.

“Nothing much,” said Thaddeus, in a moment.  “There is no one below.”

“But what could it have been?”

“I haven’t the slightest idea,” said Thaddeus, “unless it was a stray cat in the house.  The sweeping sound may have been caused by a cat scratching its collar—­or purring—­or—­or—­something.  At any rate, things appear to be all right, my dear, so let’s go to sleep.”

Thaddeus’s assumed confidence in the rightness of everything, rather than his explanations, was convincing to Mrs. Perkins, and in a very short while she was sleeping the sleep of the just and serene; but to Thaddeus’s eye there came no more sleep that night, and when morning came he rose unrefreshed.  There were two problems confronting him.  The first was to solve the mystery of the swept library floor; the second was to do this without arousing his wife’s suspicions that anything was wrong.  To do the first he deemed it necessary to remain at home that day, which was easy, for Thaddeus was more or less independent of office-work.

“I’m glad you’re not going down,” said Mrs. Perkins, when he announced his intention of remaining at home.  “You will be able to make up for your loss of sleep last night.”

“Yes,” said Thaddeus.  “It’s the only thing I can do, I’m so played out.”

Breakfast passed off pleasantly in spite of a great drawback—­the steak was burned almost to a crisp, and the fried potatoes were like chips of wood.

“Margaret seems to be unfamiliar with the art of cooking this morning,” said Thaddeus.

“So it would seem,” said Bessie.  “This steak is horrible.”

“The worst part of it is,” said Thaddeus, “she has erred on the wrong side.  If the steak were underdone it wouldn’t be so bad.  Isn’t it a pity Edison can’t invent a machine to rarefy an overdone steak?”

“That would be a fine idea,” smiled Bessie.  “And to take a Saratoga chip and make it less like a chip off a granite block.”

“I don’t mind the potatoes so much,” said Thaddeus.  “I can break them up in a bowl of milk and secure a gastronomic novelty that, suitably seasoned, isn’t at all bad, but the steak is hopeless.”