In a hidden chamber beneath an estate in Zurich, a tomblike vault is discovered containing the Unholy Trinity: Satan, the Antichrist and the False Prophet. In Paris, an elite assassin resurfaces with the intent to raze three major cities through acts of terrorism. In Rome, an old and deadly faction rises once again to remove Kimball Hayden permanently from the ranks of the Vatican Knights. In Vatican City, the pontiff continues to cling to dark ambitions that places the seat of the papacy in moral jeopardy. Once again, the Bangladeshi returns to discover his caretaker's secret, a crate that holds the Unholy Trinity. Now with the power to unleash them from their sarcophagus to spell true Hell on Earth, the elite assassin is on the move to turn the Vatican into the Kingdom of Flames. As Kimball Hayden and his team of Vatican Knights try to rise to the occasion, Kimball soon discovers that he has become the subject of a targeted killing from an old enemy and a guild that has lived in the shadows for centuries, only to emerge once again to hunt down the Vatican Knight in a final contest. With the Unholy Trinity about to raze Vatican City to scorched ruins, and as a deadly cabal hunts down Kimball Hayden with the blessing of the pope, the Vatican Knights quickly find themselves with their backs against the wall and the odds against them overwhelming.