She knew this. That philematology is the science of kissing. That Samuel Langhorne Clemens is better known as Mark Twain. That, originally, gold comes from the stars...

Madeleine Tully lives in Cambridge, England, the World a city of spires, Isaac Newton and Auntie's Tea Shop. Elliot Baranski lives in Bonfire, the Farms, the Kingdom of Cello where seasons roam, the Butterfly Child sleeps in a glass jar, and bells warn of attacks from dangerous Colours. They are worlds apart until a crack opens up between them; a corner of white the slim seam of a letter. Elliot begins to write to Madeleine, the Girl-in-the-World a most dangerous thing to do for suspected cracks must be reported and closed. But Elliot's father has disappeared and Madeleine's mother is sick.

Can a stranger from another world help to unravel the mysteries in your own? Can Madeleine and Elliot find the missing pieces of themselves before it is too late? A mesmerising story of two worlds; the cracks between them, the science that binds them and the colours that infuse them.