Pearl and Vally Cole live in a bookshop. And not just any bookshop. In 1893, Cole's Book Arcade in Melbourne is the grandest bookshop in the world, brimming with every curiosity imaginable. Each day brings fresh delights for the siblings: voice-changing sweets, talking parrots, a new story written just for them by their eccentric father.

When Pearl and Vally learn that Pa has risked the Arcade - and himself - in a shocking deal with the mysterious Obscurosmith, the siblings hatch a plan. Soon they are swept into a dangerous game with impossibly high stakes: defeat seven challenges by the stroke of midnight and both the Arcade and their father will be restored. But if they fail Pearl and Vally won't just lose Pa - they'll forget that he and the Arcade ever existed.