"This is going to be a tough nut to crack," Rick stated. "Look at that rock wall. Obviously, we'd have seen anything living that tried to climb down it, even in the darkness. If anyone had been standing up here, he'd have been silhouetted against the sky."

"There was no one on the hill last night," Scotty said positively. "I looked at every inch of it."

Barby listened to the exchange with an exasperated expression on her face. "Can't you two believe the evidence of your own eyes? The Blue Ghost appeared right under where we're standing. You can see for yourselves that nothing could be hidden by anyone to make a ghost appear. Besides, it was too real to be a trick."

"It was a ghost," Jan Miller said with quiet conviction. "Everyone has always known there was a ghost here."

Scotty shook his head. "Everyone has always known there were ghosts in a hundred places, if you want to consider all the folklore about spooks. A few people have even claimed to have seen one. But who ever heard of a haunt that put on nightly performances?"

"You have now," Barby said flatly.

"Maybe," Rick said. He didn't know why he was still skeptical. The apparition had been really blood-curdling in its apparent realness, but he still wasn't ready to buy a supernatural explanation.

Jan Miller replied with an appropriate quote from William Shakespeare.

"There are more things in heaven and on earth than are dreamed of in thy philosophy, Horatio Brant!"

Rick grinned. "That's true. No one knows better than I how ignorant I am. I can only say that I'm trying to learn. Let's climb down and look at the pool."

He led the way down the rocky slope to where the rusted iron pipe jutted from the side of the Hill, a thin trickle of water dripping constantly into the pool below. The pool was actually a catch basin in the rock.

Rick examined the pipe. It was ordinary, rusted but still sound. It held no secrets that he could see. He held his mouth under it and tasted the water. It was cold and good, typical spring water, with the taste of minerals in it. He knew from Dr. Miller that it was good to drink.

Picnickers used it regularly.

"Expect evidence to float out with the water?" Barby asked.

"Never can tell," Rick said, unperturbed. His sister, even more than Jan Miller, was an incurable romantic. If the ghost turned out to be something other than the pitiful shade of Captain Costin, she would be bitterly disappointed, Rick knew.

He got down on his knees, Scotty beside him, and they probed in the water of the rocky basin with their hands. There was a layer of brown algae in the bottom, which was to be expected. It looked dead, but when Rick sc.r.a.ped it, there was green underneath the brown.

Scotty took out his jackknife and probed with the largest blade.

Clearly, there was nothing in the basin but a solid rock bottom.

The boys' eyes met. "The pool bubbled a little last night," Rick recalled.

Scotty nodded. "I saw it, too. But there's nothing there to make it bubble."

Jan Miller shuddered. "I almost died when you two idiots scrambled up here. You went right into that awful mist!"

Rick remembered the icy tendril that had curled around his face and a little chill went through him. "It was cool," he said. "At least the Blue Ghost isn't warm. Maybe he's blue with cold."

Scotty used his jackknife to probe at cracks in the rocky hillside. It was seamed with them, but he found nothing unusual. "I give up," the dark-haired boy said, his face showing his bewilderment. "There's absolutely nothing here. So where did the ghost come from?"

"Where does any ghost come from?" Rick asked. "Same place." Their inspection should have settled it, but he wasn't ready to quit yet. To give up would mean admitting that the Blue Ghost was really a spook. He might have to admit it eventually, but not until all avenues of investigation were closed.

"Now what?" Scotty asked.

"Let's look around some more."

Barby thought this was nonsense and let them know it. "You two can prowl around all you want to," she said. "But I'm not going to get an overdose of sun spook hunting on the rocks. Coming, Jan?"

"Lunch at noon sharp," Jan reminded the boys. "We'll go help Mother.

Good luck."

Rick and Scotty watched them go, then sat down next to the pool.

"What's on your mind?" Scotty asked.

Rick shrugged. "Nothing. I haven't the ghost of an idea about this ghost."

"It was pretty real," Scotty remembered.

"Too true." It was so real that Rick almost believed in it. But he was bothered by a vague feeling that something was wrong.

"Look, Scotty. I've read plenty of ghost stories, and I've read the book by Charles Fort that Dad has in the library. Nothing was ever said about this kind of ghost. I mean, a ghost that went in for public appearances promptly at nine whenever he had an audience. Of course, there's no rule that says a ghost has to behave in any definite way, but this is too ...

well, it's too perfect, if you know what I mean."

"I do. It's almost like a show, isn't it?"

"That's it. It's a performance more than an appearance, if there's any distinction. The ghost did exactly what he's been doing. Same act."

Scotty grinned. "Why not? The act is part of the legend, and it's a pretty convincing one."

Rick c.o.c.ked an eyebrow at him. "Whose side are you on? The ghost's or mine?"

"I have an open mind," Scotty explained.

The phrase rang a bell in Rick's head. Open mind--open _mine_. Could there be some connection between the abandoned mine and the ghost? After all, the shaft was almost under them. He broached the idea to Scotty.

His pal rose. "Nothing like finding out. Are you for it?"

"I'm for it. Can we get in?"

"We'll soon see."

The boys scrambled down the hill and inspected the entrance. Boards had been nailed across the timbered opening, but the nails were rusted and the boards weathered. They could get in simply by pulling the boards loose.

"How about light?" Scotty asked. "We didn't bring a flashlight."

"We can do that later. Right now let's take a look at the entrance. That will tell us if there has been any traffic around."

The boards came off easily with the screech of old nails pulling loose.

In a few moments enough boards were pulled away to allow them to enter on hands and knees. A top board was pulled off to admit light, and they went in together, inspecting the ground closely.

"No sign of visitors," Scotty said. "Look at the dust. It hasn't been disturbed for a half century."

Rick thought his pal probably was right about the length of time. The dust was fine, and thick. No human tracks disturbed it, but the boys saw the delicate tracery where a small animal, probably a field mouse or a chipmunk, had left his spoor.

The tunnel was about eight feet high and wide enough for three people to walk abreast. Probably the lead ore had been taken out in carts when the mine was in use.