Plot summary
Brother Diaz is called to the Holy City to meet with the pope, but instead meets Cardinal Zizka, who informs him he has been chosen to lead the secretive Chapel of the Holy Expediency. In the service of the Chapel are the immortal Templar Jakob of Thorn and pirate Baptiste, who introduce Diaz to meet the imprisoned members of the congregation, referred to by Zizka as "the devils": the necromancer Balthazar, the elf Sunny, and the vampire Baron Rikard.
Alex, a thief, is rescued from a gang by Duke Michael of Nicaea, who identifies her as Princess Alexia Pyrogennetos, the rightful heir to Troy. She is taken to the Church's Celestial Palace, where the Church validates her identity at binds the Chapel of the Holy Expediency to accompany her on her journey to reclaim the throne in Troy and protect her from the four sons of Alex's recently deceased aunt, Empress Eudoxia. Not long after leaving the Holy City, Duke Marcian, one of Eudoxia's sons, ambushes the group with hybrid human-animal soldiers created by his mother. As the battle starts to go badly, Jakob is fatally stabbed while trying to unlock their wagon. Marcian then attacks Alex, but Sunny opens the wagon, releasing Vigga, a werewolf. Vigga defeats the hybrid soldiers and Marcian. When she threatens Alex and Brother Diaz, Jakob, who revives, commands her to stop, and she transforms back into her human form. Duke Michael is hurt in the conflict and heads back to the Holy City, telling Alex to trust his contact in Troy, Lady Severa.
To avoid being followed, the group heads to Venice, joining a procession of pilgrims. Apollonia, the Bishop among the pilgrims, betrays them for a reward, but Baron Rikard hypnotizes the bishop and the pilgrims while the group gets away. In Venice, Jakob and Baptiste make a deal with a crime lord, Frigo, to gain passage to Troy in exchange for retrieving a mysterious box from a cursed house. Jakob, Sunny, and Vigga are trapped by illusions in the house but saved by Balthazar, who breaks the spell remotely. They deliver the box to Frigo and set sail for Troy. Frigo betrays them and they are attacked by Duke Constans, whose galley rams their ship. As their boat sinks, hybrid soldiers board, and the group is separated. Jakob is stabbed by Constans but manages to kill the Duke before the ship submerges.
The group washes up on a nearby beach, still separated. Balthazar, Baptiste, Rikard, and Jakob find themselves on opposite in a local war and lovers' spat between Countess Jovanka and Count Radosav. They help resolve the fighting and Balthazar begins to use magic to find Alex's location. Instead, he summons a demon to remove his papal binding, which he has tried to do several times since the start of the mission. The demon is likewise unable to do so. Back at the beach, Alex and Sunny are pursued by Duke Sabbas and his bounty hunters, including a werewolf. They are in turn followed by Vigga and Brother Diaz, who form a romantic relationship. Vigga fights off some of the bounty hunters, and the four take refuge in a ruined abbey. Duke Sabbas and his hunters arrive shortly before Balthazar, Baptiste, Rikard, and Jakob. Vigga and the Duke's werewolf begin fighting, then mating. Jakob challenges Sabbas to a duel, allowing Balthazar to raise a horde of undead buried beneath the abbey. The corpses pull Sabbas into a pit. Afterward, the group rests in Sabbas's abandoned camp. Alex takes a drunk Sunny to rest, and Sunny kisses her.
The group reaches Troy, where Lady Severa welcomes them and leads them to the Pharos of Troy. While Alex prepares for her coronation, Diaz visits the athenaeum. When powerful families of Troy try to extract money in order to support Alex's claim to the throne, Diaz acts as her lawyer, contradicting each of the claims using documents from the library. Duke Arcadius, Eudoxia's last son, interrupts the event, proposing marriage to Alex instead of fighting. Michael, Severa, and Jakob endorse the idea as a political and military necessity. Upset, Alex confesses to Sunny that she is not the princess but a common thief who took on Alexia's identity after her death.
Alex is crowned and, their mission finished, the devils board a boat to leave Troy for the Holy City. In the royal apartments, Arcadius tells Alex he wants a political alliance for Troy's safety, and she agrees. However, her new handmaidens are revealed to be Eudoxia's former apprentices, killing Arcadius with ice magic. Alex manages to escape and uses the great flame in the Pharos to signal for help. She makes her way into Duke Michael's office, finding a letter from Zizka detailing a plan whereby Alex would be used as a distraction to lure out the sons of Eudoxia, then killed along with Arcadius so Michael could become emperor.
Jakob makes his way up to the apartments while Diaz, Baptiste, and Vigga fight the guards and move into a church, where she takes her wolf form and fights "the leftovers," a mass of bodyparts animated by Eudoxia. Baptiste intervenes to protect Diaz from the wolf and is killed. Jakob duels Michael, but is wounded and crushed by a statue. Balthazar discovers that Lady Severa is Eudoxia, who has transferred her soul to another body. After briefly fighting, she offers an alliance, but Balthazar chooses to stay loyal to the church, having been impressed by the strength of the papal binding. Rikard kills the four handmaiden sorceresses as they cornered Alex in the Pharos. Alex tries to escape with Sunny, but Michael stops them. Jakob arrives, tackles Michael, and they both fall into the sea.
After the attempted coup, Cardinal Zizka visits Troy to meet Empress Alexia and Brother Diaz, who is now her chaplain. Alex asks the Church to free the devils, but Zizka refuses, stating they are too dangerous. The devils are kept on Zizka's ship until the Church needs them again. Back in the Holy City, Mother Beckert and a man named Caruso are called to meet the pope, each having skills similar to Diaz and Baptiste.
