Fire spell by Laura Amy Schlitz, and published by Bloomsbury in 2012. (Note: Published under the title: Splendors and glooms by Candlewick Press in the USA). The cover of the Fire spell edition is quite striking, but it is the Splendors and glooms cover which reflects the mood of the story most accurately, in my opinion.
From the publisher (Candlewick Press):
The master puppeteer, Gaspare Grisini, is so expert at manipulating his
stringed puppets that they appear alive. Clara Wintermute, the only child of a wealthy doctor, is spellbound by Grisini’s act and invites him to entertain at her birthday party. Seeing his chance to make a fortune, Grisini accepts and makes a splendidly gaudy entrance with caravan, puppets, and his two orphaned assistants.
Lizzie Rose and Parsefall are dazzled by the Wintermute home. Clara seems to have everything they lack — adoring parents, warmth, and plenty to eat. In fact, Clara’s life is shadowed by grief, guilt, and secrets.
When Clara vanishes that night, suspicion of kidnapping falls upon the puppeteer and, by association, Lizzie Rose and Parsefall. As they seek to puzzle out Clara’s whereabouts, Lizzie and Parse uncover Grisini’s criminal past and wake up to his evil intentions. Fleeing London, they find themselves caught in a trap set by Grisini’s ancient rival, a witch with a deadly inheritance to shed before it’s too late.