The door swung in on blackness. Gathering their gear again, they slipped inside.

Alec tacked a square of heavy felt over the grate, then looked around the little entrance chamber. In front of them, stone steps led downward through an arched passage and out of sight. The faint stench already permeating the air left no doubt they were in the right place.

"Here, we'd better put these on now." Seregil pulled vinegar-soaked face rags from a leather pouch and handed one to Alec. Leaving their cumbersome cloaks, they lit their torches with a firechip and started down, Seregil in the lead.

"Why did they build it so big?" Alec whispered; the arched passage was nearly ten feet high.

"For safety. The poisonous humours that can collect down here rise. The theory is that this design lets them collect overhead, with good air below. Keep an eye on the torches, though; if they burn blue or gutter, the air's bad."

The stairway led down to a tunnel below. Narrow walkways bordered a central channel, full to the brim now with a swift, evil-smelling stream.

Turning to the right, they followed the tunnel for several hundred feet. The recent rains had swelled the flow, and it had overflowed whole sections of the raised walkway, forcing them to wade ankle deep in the foul, frigid waters.

Suddenly they heard high-pitched growling and squeaking coming from the darkness ahead. Seregil edged forward, torch held high, until they came to an iron grate fixed across the width of the tunnel.

The lower ends of the vertical bars extended down into the channel and the body of a small dog was caught against them, held there by the pressure of the stream as it flowed through. Dozens of fat, snarling rats swarmed over the carcass, tearing at it and each other. Others paddled down the channel toward the feast or perched on the crosspieces of the grate. They paid little attention to the human interlopers as they fed, beady eyes glaring red in the torchlight.

"This one is gated," whispered Seregil, driving off the closest rats with the burning torch. "It's locked up, but it's nothing we can't manage. Want to do the honors?"

"Go ahead," Alec rasped, not wanting to have to squeeze past his companion in such a narrow place.

Jiggering the lock, Seregil swung back a narrow section of grate on protesting hinges and stepped through, Alec close on his heels.

There were more rats beyond, rats everywhere. The chuckle of the flowing water and the sounds of the rats echoed in the silence as they paused at a sort of crossroads where another channel flowed into the one they were following.

Leaping the four feet to the other side, they continued on to a second hinged grate. Beyond this the way began to slope downhill noticeably.

No other tunnels intersected theirs and finally they came to a fixed grate. The ironwork was new and of the same design Alec had seen at the work site.

The broad flanges set at the four corners of the grate rested against stone knees jutting from the walls of the tunnel and were held in place by thick iron pins set in holes drilled into the stone.

"Here we are," Seregil whispered, setting down his bundle. "Light your torch from mine and go check that side."

"What are we looking for, exactly?"

"I don't know, so be thorough. It could be some fault in the iron or the stone."

Alec jumped across the channel and began his examination of the ironwork, looking first for something as obvious as bars sawn through. They seemed sound enough, however. The sockets for the pins had been sealed with rivets hammered in hot and the lower flanges, which bore the weight of the grate, rested solidly against the stone knees.

"Let's try moving it," said Seregil.

Grasping two crosspieces, they braced their shoulders against the bars and lifted. The grate lifted an inch or two.

"Push!" Seregil grunted, shaking his side of it.

But the grate was solidly held in place by the pins. Giving up, they let it fall back into place with a dull clank.

"I thought maybe he'd sawn off the lower pins,"

Seregil panted, flexing his arms. "I guess not."

"It did move, though." Alec squinted up at the flanges overhead. It was impossible to see anything from this angle, so he climbed the crossbars for a closer inspection, torch in hand.

Across the channel, Seregil was about to do the same, but his torch was burning low. Pulling a fresh one from his belt, he paused to light it from the old one. "See anything?"

"There's nearly three inches of pin exposed up here," Alec replied, clinging one-handed to the top of the bars.

"I'm no expert, but that seems like a lot. How does it look?"

"Like a metal pin." Alec held his torch closer. "No marks or cuts. Hold on.

Hey, it's melting like wax and there's—"

"Be careful!"

Searing white sparks erupted inches from Alec's face with an angry spitting sound. With a startled cry, he dropped his torch and threw an arm across his face.

"Alec! Alec, get down," Seregil yelled.

Alec crouched awkwardly, one leg jammed between the bars. Overhead, sparks still rained down from the sizzling corona of light.

Dark spots danced in front of Seregil's eyes as he launched himself across the channel. Grabbing Alec, he dragged him to the floor and tried to roll him onto his belly to smother the smoldering patches on his tunic.

"My eyes!" Alec gasped, struggling away in pain and confusion.

"Hold still," Seregil began, but Alec's foot found sudden purchase against the wall and, with a final lurch, he toppled Seregil backward into the icy channel.

Fortunately, Seregil had the presence of mind to clamp his mouth shut as he went under. For a horrifying second he tumbled helplessly against the side of the channel, unable to find the bottom with his feet. Fetching up against the grate, he righted himself and used the crossbars to pull himself back onto the walkway.

Sputtering and retching, he grasped Alec by the back of the tunic and hauled him out of range of the sparks, then held him forcibly still while the white light faded slowly to a small orange glow. One torch still burned, and by it he could see the thin pall of smoke curling lazily near the roof.

Alec groaned again, hands pressed over his face.

Fearing the worst, Seregil dug the lightwand from his sodden tool roll and pulled the boy's hands away to inspect the damage.

Alec's hair and the vinegar mask had protected most of his face from the sparks, but half a dozen tiny blisters were already bubbling up on the backs of his hands. Tears streamed down his cheeks as he turned his head from the light.

"Can you see anything?" Seregil asked anxiously.

"I'm beginning to." Alec pressed one sleeve across his eyes, then blinked. "Why are you wet?" A look of shocked realization slowly spread across his face. "Oh, no. Oh, Seregil, I'm sorry!"

Seregil managed a tight grin, trying hard not to think about the water dripping down his face toward his mouth.

"What was that light?" Alec asked.

"I don't know." Going back to the grate, he climbed up to inspect the damage. "The pin is burned completely away, stonework cracked from the heat, top of the flange warped. And whatever it was, it must work on the other side, too, or you still couldn't move the grate."

Jumping the channel, he gripped the handle of the lightwand between his teeth and climbed up to inspect the upper corner.

"Tell me again what you saw."

Still blinking, Alec came across and picked up the torch. "I held the flame close to the pin, trying to see if it had been cut. It must have been the heat, because the surface of the pin began to melt and run like wax. I think I saw something white underneath, just before it flared up the way it did."

Craning his neck cautiously, Seregil found several inches of exposed pin between the flange and the stonework above. Using the tip of his dagger, he scraped gently at the surface of the pin. Curls of some black, waxy substance shaved off easily, revealing a white layer below.