"Hello, Dad. You got him to come, then." She turned on Dr. Burrows with a self-conscious smile. "Do come down to the kitchen. Bit of a mess, but I'll put the kettle on," she said, closing the door behind them.

Dr. Burrows followed Pineapple Joe as he stomped over the tarpaulins in the unlit corridor, where the wallpaper had been half stripped from the walls.

Once in the kitchen, Pineapple Joe's daughter turned to Dr. Burrows. "Sorry, how rude, I didn't introduce myself. My name's Penny Hanson — I think we've met before." She emphasized her new surname proudly. For an awkward moment, Dr. Burrows looked so totally mystified by this suggestion that she flushed with embarrassment and quickly mumbled something about making the tea, while Dr. Burrows, indifferent to her discomfort, began to inspect the room. It had been gutted and the plaster stripped back to the bare brick, and there was a newly installed sink with half-finished cupboard units along one side.

"We thought it was a good idea to take out the chimney, to give us the space for a breakfast bar over there," Penny said, pointing at the wall opposite the one with the new units. "The architect said we just needed a brace in the ceiling." She indicated a gaping hole where Dr. Burrows could see that a new metal joist had been bedded in. "But when the builders were knocking out the old brickwork, the back wall collapsed, and they found this. I've contacted our architect, but he hasn't called me back yet."

To the rear of the fireplace a heap of soot-stained bricks indicted where the hearth wall had been. With this wall removed, a sizable space had been revealed behind it, like a hidey-hole.

"That's unusual. A second chimney flue?" he said to himself, almost immediately uttering a series of no's as he shook his head. He moved closer and looked down. In the floor was a vent about three feet by a foot and a half in size.

Stepping between the loose bricks, he crouched down at the edge of the opening, peering into it.

"Uh… have you got a flashlight handy?" he asked. Penny fetched one. Dr. Burrows took it from her and shone it down into the opening. "Brick lining, early nineteenth century, I would venture. Seems to have been built at the same time as the house," he muttered to himself as Pineapple Joe and his daughter watched him intently. "But what the blazes is it for?" he added. The strangest thing was that at he leaned over and peered down into it, he couldn't see where it ended. "Have you tested how deep it is?" he asked Penny, straightening up.

"What with?" she replied simply.

"Can I have this?" Dr. Burrows picked up a jagged half-brick from the pile of rubble by the collapsed hearth. She nodded, and he turned back to the hole and stood poised to drop it in.

"Now listen," he said to them as he released it over the vent. They heard it knocking against the sides as it fell, the sounds growing quieter until only faint echoes reached Dr. Burrows, who was now kneeling over the opening.

"Is it-?" Penny began.

"Shhh!" Dr. Burrows hissed impolitely, giving her a start as he held up his hand. After a moment he raised his head and frowned at Pineapple Joe and Penny. "Didn't hear it land," he observed, "but it seemed to bounce off the sides for ages. How… can it be that deep?" Then, seemingly oblivious to the grime, he lay down on the floor and stuck his head and shoulders into the hole as far as he could, probing the darkness below him with the flashlight in his outstretched arm. He suddenly froze and started to sniff loudly.

"Can't be!"

"What's that, Burrows?" Pineapple Joe asked. "Anything to report?"

"I might be mistaken, but I could swear there's a bit of an updraft," Dr. Burrows said, pulling his head out of the gap. "Why that should be, I just don't know — unless the whole block was built with some form of ventilation system between each house. But I can't for the life of me imagine why it would have been. The most curious thing is that the duct" — he rolled over onto his back and shone his flashlight upward, above the hole — "appears to carry on up, just behind the normal chimney. I presume it also vents as part of the chimney stack, on the roof?"

What Dr. Burrows did not tell them — did not dare tell them, because it would have appeared too outlandish — is that he had smelled that peculiar mustiness again: the same smell he had noticed on his collision with the man-in-a-hat the day before on Main Street.

Back in the tunnel, Will and Chester were finally making progress. They were digging out the soil below the sandstone when Will's pickax hit something solid.

"Drat! Don't tell me the rock carries on down here, too!" he yelled, exasperated. Chester immediately dropped his wheelbarrow and came running in from the main chamber.

"What's the matter, Will?" he asked, surprised at the outburst.

"Blast! Blast! And blast!" Will shouted. He was shocked. He had never seen Will lose his cool this way before; he was like a boy possessed.

Will increased his attack with the pickax, working at fever pitch as he struck wildly at the rock face. Chester was forced to take a step back to avoid his swings and the torrents of sil and stone he was throwing out behind him.

Suddenly Will stopped and fell silent for a moment. Then, slinging aside his pickax, he sank to his knees to scrape frantically at something in front of him.

"Well, look at that!"

"Look at what?"

"See for yourself," Will said breathlessly.

Chester crawled in and saw what had excited his friend so much. Where Will had cleared away the soil there were several courses of a brick wall visible under the sandstone layer, and he'd already loosened some of the first bricks.

"But what if it's a sewer or railway tunnel or something else like that? Are you sure we should be doing this?" Chester said anxiously. "It might have something to do with the water supply. I don't like this!"

"Calm down, Chester, there's nothing on the maps around here. We're on the edge of the old town, right?"

"Right," Chester said hesitantly, unsure of what his friend was getting at.

"Well, this won't have been anything built in the last hundred to hundred and fifty years — so it's unlikely to be a train tunnel, even a forgotten one, way out here. I went through all the old maps with Dad. I suppose it might be a sewer, but if you look at the curvature of the brick as it meets the sandstone, then we're probably near the top of it. It could just be the cellar wall of an old house — or maybe some foundations, but I wonder how it came to be built under the sandstone? Very odd."

Chester took a couple of steps backward and said nothing, so Will resumed his efforts for a few minutes and then stopped, aware that his friend was still hovering nervously behind him. Will turned and let out a resigned sigh.

"Look, Chester, if it makes you happy, we'll stop work for today, and I'll check with my dad tonight. See what he thinks."

"Yeah, I'd rather you did, Will. You know… in case."

Dr. Burrows said good-bye to Pineapple Joe and his daughter, promising to find out what he could about the house and its architecture from the local archives. He glanced at his watch and grimaced. He knew it wasn't right to leave the museum closed for so long, but he wanted to look at something before he went back.

He walked around the square several times, examining the terraced houses on all four sides. The whole square had been built at the same time, and each house was identical. But what interested him was the idea that they might all have the mysterious ducts running through them. He crossed the road and went through the gate into the middle of the square, which had at its center a paved area surrounded by some borders of neglected rosebushes. Here he had a better view of the roofs, and he pointed with his finger as he tried to count exactly how many chimney pots there were on each one.