He was interrupted by Sandy who had come to the door.  “The phone call’s for you, Dad.  Long distance from Washington.”

Bud groaned as Mr. Swift went off to take the call.  “It’s a conspiracy,” Bud said.  “Everyone’s ganging up to keep us from finding out about that mysterious visitor!”

Tom grinned.  “We lasted through an earthquake this afternoon, pal,” he said consolingly.  “I guess we can last through a phone call.”

Inwardly Tom was as impatient as Bud about the exact nature of the message.

Several months ago, the space creatures had sent their first communication in the form of mathematical symbols carved on a black missile which had landed on the grounds of Swift Enterprises.

Tom and his father had decoded the symbols and beamed out a reply over a powerful radio transmitter.  Later messages had been picked up by radio telescope and converted to appear as symbols on the oscilloscope screen.

“Sandy must know what it’s all about,” Bud broke in.  “She’s the one who first mentioned the visitor.”

“Of course I know,” Sandy said mysteriously.  “So does Mother and so does Phyl.  But don’t think we’re going to give it away!” she added teasingly.

Tom and Bud cajoled the two girls and Mrs. Swift for further information.  But Sandy and Phyl only shook their heads, obviously enjoying the situation.

“At last we’re getting back at them for the way they’ve neglected us!” Phyl said, her brown eyes sparkling with laughter.

“Come on, Mother!” Tom said.  “Be a sport.  You tell us!”

But Mrs. Swift too shook her head.  “I’m sorry, Tom,” she demurred gently, “but I think the girls are right.  I’ll say this much, though,” she relented, “it will be the biggest challenge that Tom Swift Jr. and Sr. have ever faced!”

“Whew!” Bud remarked as the two boys glanced at each other.  “That must mean it’s plenty big news!  It would have to be, skipper, to top all the other jobs you and your dad have taken on!”

Conquering outer space, probing the ocean’s secrets, drilling to the earth’s core—­these were only a few of Tom Swift’s many exciting exploits.

In his first adventure, Tom, in his Flying Lab, had gone to South America to fend off a gang of rebels seeking a valuable radioactive ore deposit.  In his most recent challenge, Tom had defied the threats of Oriental killers determined to ferret out the secret of the Swifts’ latest space research.

As the two boys silently recalled the exciting events of the past months, Mr. Swift returned to the living room.

Tom and Bud leaned forward in their chairs.  “Well, boys,” Mr. Swift said, “as I started to tell you, the space receiver picked up a message today from our unknown planetary friends.  The message informed us that they are sending a visitor to earth—­a visitor consisting of pure energy!”

“Energy?” Tom was startled.  “I don’t get it, Dad!”