Her new novel is Sepulchre.
From a Q & A at Mosse's website:
Labyrinth was set in Carcassonne, in southwest France, and you return to the same region in Sepulchre, albeit centuries later. What is it about that region that inspires you as an author?Read the full interview.
Eighteen years ago now my husband and I bought a tiny, biscuit-coloured house in the medieval fortress city of Carcassonne, in the shadow of the walls of the 13th century Cité. The moment I saw it, I fell in love – with Carcassonne in particular and with the Languedoc in general, the name given to the region of southwest France bounded by the Atlantic Ocean to the West, the Mediterranean Sea to the South and the great wall of the Pyrenees to the south west. When I’m there, my imagination runs riot. It’s a combination of the outstanding, imposing, physical beauty – the endless blue sky, the wild weather than shifts from brilliant sunlight to black thunder clouds in a moment, the untamed garrigue, the mountains – and the fact that history lies littered all around. The ancient labyrinthine caves with Pre-Historic paintings, the Roman baths and roads, for this book, the Celtic legacy and the Visigoth history of the 5th, 6th and 7th centuries AD. It would be hard for any author, with such materials to work with, not to want to people the real landscape with imaginary characters. This time, focusing on the 19th century in Sepulchre rather than the 13th as in Labyrinth, it gave me the opportunity to go back to some of the places (and some of the characters) about which I’d written and see how time had changed them.
The Page 69 Test: Sepulchre.
--Marshal Zeringue