Fire Spell by Laura Amy Schlitz

We open the book to find an old witch Cassandra dreaming of being burned alive.  She wakes remembering a man called Grisini who had told her the opal that gives her her magic would burn her alive.  She tries to smash the stone, then...

We shift to London in the autumn of 1860.  Clara is a upper class young girl hoping that Grisini the puppeteer will be allowed to come to her birthday party.  She lives in material wealth but abject emotional poverty, the only survivor of the cholera that took her 4 siblings including her twin brother.  Her mother's grief makes her home a haunted melancholy place, Clara has to be silent and never to be a child.

Lizzie-Rose and Parsefall are orphans, employed and sometimes fed by Grisini.  Parsefall is learning to play the puppets, Lizzie-Rose does the fetching and carrying.  Dirt poor and unloved they marvel at Clara's house as they bring the puppet stage in.  Paresefall has his mind on petty theivery, but Grisini has something much worse in mind and the children find themselves unwittingly caught up in his spell casting and ancient feud with Cassandra.

A lovely well written book, you can really feel the texture of London both from the viewpoint of Parsefall and Lizzie-Rose struggling to stay alive and Clara who has the money to pay road sweepers to clear the roads of horse dung for her should she step down from her carriage.  Schiltz conjures the cold, the filth, and the suspense as the narrative hurtles onward.  A great read for I would say 9-13 year olds.