One mutt lifted his head and pricked his ears. The second dog used the opportunity to seize a rank-smelling fish head from the trash heap and bounded away with his prize. Then he, too, paused, whining. His jaws opened and the moist fish head fell to the slick street. The rumble grew more ominous, a different sort of growl.

The two dogs snarled at the sound that seemed to come from everywhere beneath and around them, then they scuttled away in fear. The second mutt doubled back to snatch up the fish head, then sprang down the alley just as the sound reached an explosive roar.

A dark brick wall at the opposite end of the alley split and broke as something huge, black, and mechanical hammered its way up from beneath the streets, knocking bricks and timbers apart. Walls fell, brushed aside from the leviathan as if they were little more than dust and dry leaves.

Both dogs ran for their lives as the immense subterranean machine roared and clanked after them.

Though he had been deeply asleep, immersed in dreams of playing in the park with his father on a Sunday afternoon, Bartholomew Dunning sat up quickly in bed. The pallid six-year-old boy clutched an old woolen blanket and stared into the faint light that came through the window of his cellar bedroom. On a narrow brick windowsill above the bed, his tin toy horse and buggy shuddered and rattled, as if they had come alive.

The rumbling made the entire tenement shake. Dust sprinkled down from the ceiling, captured in the hazy moonlight that penetrated the fog.

Bartholomew wanted to call out for his father, but he knew Constable Dunning would be out walking the streets, keeping London safe, as he did every night… all night. But right now the boy wanted his father. He pulled the blanket up to his chin, hoping to hide. But the noise grew louder.