Scrivener's Moon by Philip Reeve

The final adventure in Philip Reeve's brilliant Fever Crumb trilogy.

The Scriven people are brilliant, mad -- and dead.

All except one, whose monstrous creation is nearly complete -- a giant city on wheels. New London terrifies the rest of the world, and an army of mammoth-riders gathers to fight it. Meanwhile, young Fever Crumb begins a hunt for Ancient technology in the icy strongholds of the north. She finds a mysterious black pyramid full of secrets. It will change her world forever.

Scrivener's Moon follows Fever Crumb and A Web of Air to complete one of the most exciting and inventive fantasy adventures series ever written.