SOME DAYS LATER, The Three Investigators were meeting in their headquarters, a converted trailer hidden behind towering piles of lumber and scrap iron in The Jones Salvage Yard. Bob had just read a letter that had arrived that morning from a woman in Malibu Beach who wanted them to find her missing dog when the telephone rang.

Their private phone, paid for by their earnings from odd jobs around the salvage yard, didn’t ring often. When it did, it always promised excitement. Jupiter grabbed it.

“Hello,” he said. “Three Investigators, Jupiter Jones speaking.”

“Hi, Jupe.” The hearty voice of Alfred Hitchcock blared into the office from the loudspeaker Jupe had hooked up. The famous mystery novelist had taken a real interest in the boys. He introduced their cases for them and from time to time found new mysteries for them to solve.

“I’m glad I caught you in,” Mr. Hitchcock went on. “I wanted to let you know that you’ll soon have a visitor.”

“A visitor?” Jupiter repeated. “Is this in reference to a new case?” His eyes sparkled.

“No hints,” said the writer. “I’ve promised not to tell you anything beforehand. I did have a long talk with your visitor and gave you an excellent recommendation. All I can tell you is that you’re about to get a surprising invitation. I just wanted to warn you. Got to go now. Good-bye.”

He hung up, and so did Jupiter. The three boys stared at each other.

“Do you think it’s another case?” Bob asked.

They had no time to speculate, for at that moment the voice of Mathilda Jones, Jupiter’s aunt, came booming in through Headquarters’ open skylight.

“Jupiter! Out front! You have a caller.”

A moment later the boys were scrambling out through Tunnel Two, the big pipe that led from beneath the trailer to a hidden entrance in the workshop section of the yard.

From there it took them only a moment to thread their way around piles of junk to the office.