On the trail of the Cathars' secret.

South of France. Cassiopée Vitt has embarked on the renovation of a 13th-century castle. During the work, a mysterious gold box adorned with the cross of Languedoc is found in a trench. Inside, an illuminated manuscript, written in Occitan, which seems to link everything to the Cathars. While a secret society is ready to do anything to get its hands on it, Cassiopée engages in a race against time to decipher its enigmas. Soon, she discovers that its pages conceal an encrypted map, which will put her on the trail of the Cathars' best-kept secret.

After Cotton Malone, the hero of Steve Berry's novels, it's his sidekick Cassiopée Vitt's turn to take center stage. From Carcassonne to Montségur, via Toulouse, the authors take us on a thrilling journey through history, religion, and esotericism, following in the footsteps of the Cathars, declared heretics by the Pope in 1208 and whose secrets are still numerous.