only scientists who know the secret of the nuclear engine. If enemy agents kidnapped him, he may have revealed the secret. A foreign power could be building a Firebird right now!â
Frank said, âYou mentioned that someone had been after Dr. Jenson in this country.â
Professor Young nodded. âA neighbor noticed a car with Florida plates parked outside his house after he left. And the police discovered that his home had been broken into and ransacked. Also, telephone company records show that a call was made from there that same night to a pay phone in Florida near the Space Flight Center.â
âSo thatâs why Dadâs been concentrating on the case down in Florida!â Joe said.
âExactly. But he wanted all aspects of the case covered and decided his sons could handle the investigation here at the Aerospace Lab. So here you are.â
âAnd weâve brought Chet,â Frank said. âHeâs helped us many times before and is reliable.â
âThatâs fine,â Young said. âI trust your judgment.â
Chet grinned and said he would do his best to help the Hardys crack the case.
The professor continued. âYour task is to investigate all possible leads at the lab and see if you can find the clue you need to solve the mystery while your father does the same at the Space Flight Center. I have some information that might help you.â
âOh?â Frank asked. âWhat is it?â
Youngâs answer surprised him. âJenson and I received a warning letter and threatening phone calls. Here, Iâll show you.â
He reached into a drawer and took out an envelope. Removing the letter, he handed it to Frank. Joe and Chet craned their necks to see it. The message was crudely pieced together from words out of a newspaper.
It said: Kill the Firebird or else!
âSomeoneâs trying to sabotage your rocket!â Joe exclaimed. âThey donât want it to be launched.â
âThatâs right, and whoever wrote the letter means business.â
âProfessor,â Frank said, âdo you realize that you may be in great danger yourself?â
âEveryone here is aware of that. I have been assigned a personal bodyguard, without whom I do not leave the building. I donât want you to worry about me. Just find Dr. Jenson!â
Frank was about to say something when he heard a noise outside the door.
âAn eavesdropper!â Frank thought. Leaping out of his chair, he strode to the door and swung it wide open.
Smoky Rinaldo was standing there!
âHi,â Frank said. âAre you interested in our conference?â
Smoky looked surprised. âI didnât know a conference was going on in Professor Youngâs office. When I heard voices, I stopped momentarily to see if I should come in or not.â Glancing past Frank, he addressed Young. âI canât tell if the fuel is getting hot enough. Would you mind checking it when you have a chance?â
âIâll be right along, Smoky,â the professor promised. Then he said to the boys, âIâll phone the Nassau Club and make arrangements for you to stay there while youâre in Princeton. Itâs on Mercer Street.â
Young made the reservations, then went with Smoky to the atomic reactor while Frank, Joe, and Chet drove to the Nassau Club. The driveway curved in a semicircle past the steps leading up to the front door of the stately building.
Frank parked the car. âDo you think Smoky was eavesdropping?â he asked as the boys got out.
âIâm inclined to think heâs honest,â Joe said. âBut weâll keep an eye on him.â
The boys entered the building and went to the front office to see about their room. Frank inquired while Joe and Chet looked around.
A hallway led through the first floor to a coatroom at the rear. Members of the club were seated in the reading room to the left, scanning the