Two orphans, Pedrock and Boo Boo, are sent to live in the sinister village of Darkwound. There they meet and befriend the magical and dangerous Mr Loveheart and his neighbour Professor Hummingbird, a recluse who collects rare butterflies. Little do they know that Professor Hummingbird has attracted the wrath of a demon named Mr Angel-Cakes.

One night, Mr Angel-Cakes visits Boo Boo and carves a butterfly onto her back. Boo Boo starts to metamorphose into a butterfly/human hybrid, and is kidnapped by Professor Hummingbird. When Mr Loveheart attempts to rescue her with the aid of Detective White and Constable Walnut, they are turned into butterflies.

Caught between Professor Hummingbird and the demon Angel-Cakes, Loveheart finds himself entangled in a web much wider and darker than he could have imagined, and a plot that leads him right to the Prime Minister and Queen Victoria herself . . .