Tom and Ned put in some busy days, arranging the phonograph attachment.  It was easy, compared to the hard work of sending a picture over the wire.  They paid several visits to Mrs. Damon, but she had no news of her missing husband, and, as the days went by, she suffered more and more under the strain.

Finally Tom’s new invention was fully completed.  It was a great success, and he not only secured pictures of Ned and others over the wire, as he talked to them, but he imprinted on wax cylinders, to be reproduced later, the very things they said.

It was a day or so after he had demonstrated his new attachment for the first time, that Tom received a most urgent message from Mrs. Damon.

“Tom,” she said, over the telephone, “I wish you would call.  Something very mysterious has happened.”

“Mr. Damon hasn’t come back; has he?” asked Tom eagerly.

“No—­but I wish I could say he had.  This concerns him, however.  Can you come?”

“I’ll be there right away.”

In his speedy monoplane Tom soon reached Waterford.  Ned did not accompany him this time.

“Now what is it, Mrs. Damon?” asked the young inventor.

“About half an hour before I called you,” she said, “I received a mysterious message.”

“Who brought it?” asked Tom quickly.

“No one.  It came over the telephone.  Someone, whose voice I did not know, said to me:  ’Sign the land papers, and send them to us, and your husband will be released.’”

“That message came over the wire?” cried Tom, excitedly.

“Yes,” answered Mrs. Damon.  “Oh, I am so frightened!  I don’t know what to do!” and the lady burst into tears.

CHAPTER XVIII

ANOTHER CALL

Tom Swift, for the moment, did not know what to do.  It was a strange situation, and one he had never thought of.  What did the mysterious message mean?  He must think it all out, and plan some line of action.  Clearly Mrs. Damon was not able to do so.

“Now let’s get at this in some kind of order,” suggested the youth, when Mrs. Damon had calmed herself.  It was his habit to have a method about doing things.  “And don’t worry,” he advised.  “I am certain some good will come of this.  It proves one thing, that’s sure.”

“What is it, Tom?”

“That Mr. Damon is alive and well.  Otherwise the message would not have said he would be ‘released.’  It wasn’t from anyone you know; was it?”

“No, I’m sure I never heard the voice before.”

Tom paused a moment to think how useful his photo telephone and phonograph arrangement might have been in this case.

“How did the telephone call come in?” inquired the young inventor.

“In the usual way,” answered Mrs. Damon.  “The bell rang, and, as I happened to be near the instrument, I answered it, as I often do, when the maid is busy.  A voice asked if I was Mrs. Damon, and of course I said I was.  Then I heard this:  ’Sign the land papers, and send them to us, and your husband will be released.’”