Cluny swallowed hard, and the men stood silent. Jupiter stared round in the dark.

“Bob! Pete!” he called.

His voice echoed off the high walls of the quarry, ghostly in the night. The echo seemed to go on and on and changed suddenly into a different sound:

“Help! Jupe! We’re in here!”

They all froze.

“It’s them!” Cluny cried.

The voices came again. “Jupe! In here!”

“Look!” Professor Shay said. “A light in the shack!”

Cracks of light had suddenly appeared in the old shack, outlining a door and windows. Jupe scrambled down to the terrace the shack was on, followed by the others. He ran to the door and started rattling the padlock. From inside, Pete yelled,

“The front window, First! Unbar the shutter!”

Rory jumped to the window, removed the bar that held the shutters closed, and threw them open. Bob and Pete grinned out.

“Boy,” Pete said, “we thought we were stuck here for the night — or worse.”

“Someone was trying to come in after us!” Bob exclaimed. “That’s why we had the lights out. He tried the padlock, then he started to unbar the shutters.”

“Stebbins, the scoundrel!” Professor Shay said.

“He must a’ locked you in there,” Rory decided. “Was coming back for who kens what devilment when we scared him off.”

“Come out, boys,” Hans said.

Bob shook his head. “No, you climb in! We’ve got the last clue in here!”

Excited, they all climbed in one by one. Hans could barely fit in through the window. Inside the small office Bob and Pete showed them the file folder open on the desk.

“Special order number 143” Jupiter read aloud. “For A. Gunn, ship to yard, ten square-cut matched monument stones. Granite” Jupiter looked up. “Ten monument stones?”

“Adding up to a ton of stone,” Pete said. “Two hundred pounds a stone. What did old Angus want with ten big stones? Did he build some kind of monument?”

Jupiter shook his head in bewilderment.

“There’s nae a monument at Phantom Lake,” Rory said.

“Perhaps somewhere else?” Professor Shay asked.

“A monument built for Laura in some town?” Cluny guessed.

“No,” Jupiter said slowly. “I’m convinced Laura’s surprise is at Phantom Lake — somewhere. The journal couldn’t mean anything else the way Angus wrote it. He always came home to work on Laura’s surprise.”

“Then whatever he built, boys,” Professor Shay said, “is hidden! It must be that. Hidden at Phantom Lake so cleverly that no one has ever — ”

“Or,” Bob said, “so obvious we just don’t see it! stumbled over it!”

Maybe we look at it all the time, like Poe’s purloined letter, and don’t see it because it’s right in front of us!”

“There must be something we don’t yet know,” Professor Shay said bitterly.

“There’s one thing I know,” Pete said. “I know it’s late, and I’m hungry. Let’s go home and eat, fellows.”

They all laughed.

“Let’s eat at my house, guys,” Cluny urged. “You can call your folks. Mum makes a swell dinner, and we can try to puzzle it all out!”

“That sounds like a sensible suggestion.” Professor Shay smiled. “If Mrs. Gunn doesn’t mind feeding an over-age treasure-hunter.”

“I know she won’t, Professor,” Cluny said.

They made their way back round the quarry and up to the bikes and cars. Bob and Pete loaded their bikes into the truck, and all four boys got into the back. As they drove off, Pete suddenly spoke once more.

“I know something else, too, First,” he said to Jupiter. “You said this case was maybe like a jigsaw puzzle — all the pieces go together to make the answer.”

He grinned. “Well, now we’ve got all the pieces, I guess. All we have to do is put them together!”

Mrs. Gunn fussed over the boys and the three men until they had eaten their dinner. Only then would she let them gather in the living-room to talk. Professor Shay began to pace the big room.

“We must solve the riddle, boys, or young Stebbins and that Java Jim will steal the treasure,” the professor said. “It’s clear now that they are working together.”

“We haven’t proved that, sir,” Jupiter said thoughtfully. “But I agree that we must try to solve the riddle. We have all the pieces now — the journal trips and the letter — and I’m certain that old Angus planned a puzzle Laura could solve.”

“Ay,” Rory said, “I’ll admit ye could be right — but it’s a puzzle intended for one person a hundred years ago. Ye’ve tried, boys, but as I said from the start, it’s no’ solvable today!”

Cluny said hotly, “You sound like you don’t want us to find the treasure, Rory!”

“Find it, then, and be hanged wi’ ye!” Rory said sullenly.

Jupiter held the old letter of Angus Gunn’s in his lap and opened the thin journal. Bob, Pete, and Cluny gathered round.

“We now have all four steps in old Angus’s last course, the days that built Laura’s surprise,” Jupiter summarised. “What we must do now is try to see what they point to, and how they relate to the secret of Phantom Lake — that is, the legend of the phantom itself. And we must discover what a mirror has to do with the secret.”

“Sure,” Pete groaned. “That’s all we have to do!”

Jupiter ignored the Second Investigator. “First, Angus went to Powder Gulch for sluice timber, supports, and miners. A big job, we decided, from the amount of food he bought.

“Second, he went to Cabrillo Island, made some proposal that the squire of the island agreed to, and came away with a load in his boat. He brought something from the island to here.

“Third, he bought ten two-hundred-pound, square-cut monument stones from the Ortega brothers and carted them here.

“Fourth, he bought something from Wright and Sons in Santa Barbara as a last touch to Laura’s surprise. Something normally found on a ship, almost certainly, since that’s all Wright and Sons sold in those days. Something with a brass plate with their name on it.”

Jupiter stopped. Rory laughed where he sat near a front window.

“Ye put all that together,” the Scotsman said, “and then ye chase a phantom that’s no’ even in this country! When ye catch your ghost, why, ye tell him to look in a mirror!”

“Gosh!” Bob flushed. “It does sound sort of — ”

Mrs. Gunn frowned at Rory and turned to Jupiter. “While you were all at the quarry, I looked and looked, but I couldn’t find anything in the house with a Wright and Sons brass plate on it. I can’t imagine what it would be.”

Jupiter shook his head bleakly. “Whatever it was, I’m convinced that all the items that Angus bought have to add up to one thing. All of them go together, somehow, to make Laura’s surprise. It has to do with what Angus loved at home, as the letter says. But,” he finished lamely, “what could it be?”

“Something pretty big,” Cluny said hopefully.

“What did Angus do with all that sluice timber and those men?” Professor Shay asked. “Where is all the timber?”

“And where did he put a ton of big stones?” Bob added. “I mean, ten monument stones are pretty hard to hide.”

“Hey!” Pete cried. “What do miners do best? Jupe, you say always think of the most simple explanation. What a miner does best is — dig! They dug a big hole, used the sluice timber for supports and the big stones, too! Maybe an underground room!”

Professor Shay stopped pacing. “A big hole? In the ground?”

“Why not?” Pete insisted. “That’d be a good place to hide a treasure. Maybe Angus bought a brass handle from Wright and Sons, or a lantern for the hidden room!”

“But what would he have needed from Cabrillo Island?” Jupiter asked. “And I don’t think a hidden underground room would have been much of a surprise for Laura. Remember, as far as we can tell, Angus planned the surprise first and added the treasure to it later.”

Professor Shay hadn’t moved since Pete suggested the big hole in the ground. Now he walked over to Rory near a front window.