They followed the flow of the sludge for another hour until the tunnel widened into a massive junction room. In the center of the room was a spiral staircase made of wrought iron, winding up around a central pillar.
But it wasn't unguarded.
Perched on the railing of the staircase were birds. Not Magpies. These were Owls.
They were huge, with feathers the color of dust and ash. They wore thick, round spectacles on chains. They were perfectly still, like statues.
"The Silence Keepers," Mittens whispered, pulling Noah into the shadows. "Don't make a sound. If they hear you, they shush you."
"Shush me?"
"With a sonic blast that can liquefy your eardrums. They guard the Library District. That staircase leads up to it."
Noah looked at the stairs. It was the only way up.
"We have to sneak past them," Noah mouthed.
He took off his boots. He tied the laces together and hung them around his neck. He moved forward in his socks.
The floor was wet and slippery. Noah took a step. Squish.
One of the Owls rotated its head 180 degrees. Its eyes, huge and yellow, scanned the darkness.
Hooooo?
Noah froze. He held his breath until his lungs burned.
The Owl turned back.
They crept forward. Step by step. Noah moved like a ghost. He reached the stairs. The metal was cold against his feet.
He started to climb. Mittens followed, his paws silent as death.
They made it past the first Owl. Then the second.
On the third landing, Noah's boot swung on its lace and tapped against the metal railing.
Clink.
It was a tiny sound. Barely a whisper.
But in the Undercity, it sounded like a gunshot.
Six heads swiveled instantly. Six pairs of yellow eyes locked onto Noah.
"SHHHHHHHHHHH!"
The sound hit him like a physical blow. A wall of compressed air slammed into him, throwing him back against the wall. His ears rang with a high-pitched whine.
"Run!" Mittens yelled, abandoning stealth.
Noah scrambled up the stairs, ignoring the pain in his head. The Owls took flight, their wings silent, swooping down like bombers.
"SHHHHHHHHHHH!"
Another blast hit the stairs behind him, warping the metal.
"Quiet! Silence in the Library!" they screeched.
Noah pumped his legs, taking the stairs two at a time. He saw a trapdoor at the top. Light was leaking through the cracks.
He reached it. He slammed his shoulder against the wood. It groaned but didn't open.
"Open it!" Mittens shouted, dodging an Owl's talons.
Noah shoved again, screaming with effort. "I! WILL! NOT! BE! QUIET!"
The wood splintered. The trapdoor flew open. Noah and Mittens tumbled out onto a floor of polished marble, slamming the door shut behind them and dragging a heavy bust of a cat philosopher over it to weigh it down.
Below, the thumping and shushing continued for a moment, then faded.
They lay on the floor, gasping for air.
"I hate birds," Mittens wheezed. "I really, really hate birds."