The Railway Mania has gripped England. The Iron Horse rules supreme, and endlessly proliferating railway lines have created the shadowy zone known as The Underarches, that lurks beneath the very boot-heels of progress.

Welcome to a steam-driven Victoriana where gryphons are real and children's snow-globes are powered by nasty-minded little imps.
A world where a powerful new drug called spike beguiles high and low society alike.

Alexia Burgundy, owner of a struggling railway company bedevilled by bad luck, is reluctantly drawn into the sphere of Jack Hammond, proprietor of the fabulously successful Hammond & Hill Railway Co., sole producers at their Arleyvale coalmine of the revolutionary new fuel called Black Adamantine. The journalist Daniel Benjamin, meanwhile, persists in digging ever deeper into the circumstances surrounding a mysterious accident at Hammond's mine.

All the while, an entity both ancient and implacable stirs in the bowels of the earth beneath Arleyvale Colliery...