On the brink of death, the Duke of Milan entrusts his only heir to the church, which is guarding a thousand-year-old secret

It is the early fifteenth century, and the Italian peninsula is ravaged by war. While Milan fights for its political and economic life, Duke Filippo Maria Visconti lies on his deathbed with no heir to succeed him. But the old nobleman has a secret: He has a son.

Visconti hands over the one-year-old child to the archdeacon Onorio, who agrees to keep him safe. Little does young Niccolò know that when he comes of age, he will inherit the great Visconti fortune and become the city's next duke.

Years later, in the shadows of a new cathedral, the members of a secret brotherhood practice alchemy and plot court intrigues, working to fulfill the ancient prophecy of the goddess Belisama. The brothers, sustained by blind faith, will do whatever it takes to achieve their Grande Opera, but first they need peace in the city, and Niccolò is the only one who can help. But when he starts to witness mysterious rites and killings, Niccolò will be forced to reconsider his destiny.