Pan The Burning Chambers (The Joubert Family Chronicles).

Carcassonne 1562: Nineteen-year-old Minou Joubert receives an anonymous letter at her father’s bookshop. Sealed with a distinctive family crest, it contains just five SHE KNOWS THAT YOU LIVE. But before Minou can decipher the mysterious message, a chance encounter with a young Huguenot convert, Piet Reydon, changes her destiny forever. For Piet has a dangerous mission of his own, and he will need Minou’s help if he is to get out of La Cité alive. As the religious divide deepens in the Midi, and old friends become enemies, Minou and Piet both find themselves trapped in Toulouse, facing new dangers as sectarian tensions ignite across the city, the battle-lines are drawn in blood and the conspiracy darkens further. Meanwhile, as a long-hidden document threatens to resurface, the mistress of Puivert is obsessed with uncovering its secret and strengthening her power.