Madame Vastra, the fabled Lizard Woman of Paternoster Row, knew death in many shapes and forms. But perhaps one of the most bizarre of these was death by snow....

On a cold day in December, two young boys, tired of sweeping snow from the workhouse yard, decide to build a snowman - and are confronted with a strange and grisly mystery. In horrified fascination, they watch as their snowman begins to bleed....

The search for answers to this impossible event will plunge Harry into the most hazardous - and exhilarating - adventure of his life. He will encounter a hideous troll. He will dine with a mysterious parlour maid. And he will help the Great Detective Madame Vastra save the world from the terrifying Devil in the Smoke.