Arlo Goodman lives with his Uncle Avery in a run-down flat above their bookshop. He has no friends, except for his pet mouse, Herbert.

But when a girl called Lisette bursts into the shop and begs him to hide her from a murderer, Arlo's life changes forever.

He's swept up into an adventure involving kidnappers, car chases and a story in The Book of Wondrous Possibilities, where Arlo and his skymouse battle dragons. But can Arlo find the courage to battle an even greater enemy, who threatens to destroy everything he loves?