The Secret Book is a Macedonian feature film combining the detective, thriller and conspiracy fiction genres, based on "Secret Book" (French: Le Livre Secret, Macedonian: Тајната книга), a real mystical book written by the Bogomils with Glagolitic letters (the first Slav alphabet, made by SS. Cyril and Methodius).

Bogomil ideas, carried back to France and Italy from the Balkans by refugees or returning crusaders in the 11th century, became the basis of the Cathar heresy. Like them, the Bogomils were massacred by the church and their name almost burned from history.