A routine flight aboard the airship Tristan turns deadly when the craft is hijacked by the vampire Alfred, a member of the radical group, Fleurs du Mal. Unless Alfred's demands are met, he intends to crash the Tristan into the heart of Rome. Only Abel Nightroad, a passenger on the ship and a touring priest for the Vatican, stands between the vampire and the destruction of the Holy See.

While investigating the activities of the Fleur du Mal, Father Nightroad encounters a young girl with strange and dangerous abilities. And when the girl attempts to flee, Abel must turn against his own comrades in order to save her life and prevent her from falling into enemy hands.

Abel Nightroad journeys to Ishtvan, a city where the tenuous balance of power between the Human and Vampire worlds is threatened. With the vampiric Count Gyula secretly preparing a weapon of mass destruction and the Vatican's Sister Esther carrying out her own personal war, Abel finds himself caught between a rock and a hard place.

With Esther and Abel his prisoners, Count Jula reveals his plan: to use the Star of Sorrow to rain destruction down on the human race in revenge for his wife's murder. But the mysterious order of Rosen Kreuz has its own plot for twisting Jula's scheme to achieve their evil ends. If Abel can't stop them, the world could face Armageddon all over again.

Father Abel Nightroad escorts Sister Esther to Rome, where she meets Lady Caterina Sforza. While there she also meets William Walter Wordsworth, Father Havel, and Sister Noelle Bor, who all do their part to welcome her into the AX. While lost on the grounds, she encounters a young boy crying, who later turns out to be Pope Alessandro. With this being her introduction into the ways of the AX, has Sister Esther gotten herself into more than she can handle?

A murder on holy ground has taken place in Amsterdam, and Lady Caterina sends in the mysterious Father Hugue, also known as "Sword Dancer", to investigate. The local leader of the vampires, Cabel, knows the he and his followers are not responsible, but only the unconscious memories of Agnes can help him prove it. But with so much at stake on the investigation's outcome, no one can be trusted and no one is safe.