After Cardinal Ricardo Rossi is murdered, Lucas discovers documents referring to an "eighth seal" never mentioned in biblical records. He joins forces with Sister Valentina, the cardinal's niece, and Matteo di Luca, a Vatican official with his own agenda against the Custodes Sigilli—a secret organization protecting the Church's darkest secrets. Their quest reveals that the Eighth Seal isn't an object but a person born in each generation with the ability to perceive reality beyond human constructs, potentially severing humanity's connection to the divine. Lucas learns his deceased wife Sarah was the previous Eighth, murdered by the Custodes, and that Valentina is the current one.