After rescuing Oz from his execution at the hands of Oswald, Gilbert begins leading Oz through Pandora's catacombs in search of St. Luca's Gate in order to get far enough from the Baskerville Clan and their potential executions. After continuously arguing over what would be best for Gil, the two are joined by Oscar Vessalius, intent on traveling to St. Luca's Gate with Gil and Oz. In reality, Oscar had been sent to kill Jack by Xai, leaving Oscar confused and fearful of what's to come.
Several members of Pandora manage to catch up with the two, after having been sent to find and kill Oz and Gilbert. The Pandora members had only complied because they fear Oswald will end their own lives, but in the end Gilbert manages to kill them all with the help of Raven, in order to protect Oz.
Meanwhile, Rufus informs Oswald of Pandora's search being undertaken in Pandora's catacombs, explaining that if Pandora's search continues to proceed without force applied against Oz and Gilbert, they would soon have the upper hand and be able to corner then in Pandora's catacombs. Xai interjects, saying that it is likely that Gil was trying to head towards St. Luca's Gate with Oz in order to escape Pandora. Another Baskerville identifies Xai to Oswald and questions the purpose of St. Luca's Gate. Xai elaborates the purpose of St. Luca's Gate being an emergency escape route for the Four Great Dukes, but because of how rare St. Luca's Gate is used, a Key to the Abyss is necessary to access it.
Xai's explanation prompts Lottie to yell at Rufus for having not said anything about St. Luca's Gate. Rufus justifies his actions by stating that he had thought that he was going to be killed, so to have said anything about St. Luca's Gate would have been foolish, as it would have prevented him from being able to use St. Luca's Gate in secret later, if the need arose. Xai, thinking of his younger brother, whom he had sent to kill the container of Jack Vessalius' soul, mentions that it is possible that Oscar had joined forces with Oz and Gilbert, which left no doubt in his mind that the three of them would be Hell-bent on finding St. Luca's Gate.
Oswald takes a moment to ponder Xai's revelation, leaving Oswald wondering why Xai is so willing to sell out his family, despite not being a true Baskerville. Xai tells Oswald that his goal has always been to destroy Jack for all that he's done to the Vessalius Dukedom, thus meaning that the container for Jack's soul (Oz) is nothing more to him than a medium for his hatred.
Meanwhile, after the confrontation with the Pandora members, Oscar draws his gun, whilst Gil draws his own gun and demands that his target not move another muscle. Gil had been talking to Jack, whom Gil was now aware had taken over Oz again. Jack was impressed with Gil's observation, stealing Oscar's gun from him and running, revealing to Gil Oscar's intention to kill him, as well as taunting Oscar about the deaths of his wife and child while running through the catacombs. Oscar manages to tell Gil that the path to St. Luca's Gate is a lot like a maze, and despite knowing the path, it wouldn't make a difference if they lost Jack.
Eventually, Oscar manages to corner Jack, pinning him to the wall. Jack shoots Oscar in the ear as a failed attempt to kill him, Oscar pinning Jack to the wall and declaring that he intended to kill destroy what's left of Jack. Long after the confrontation with Jack, Jack attacks Oscar with Oz's power in an attempt to destroy Oscar and make it so nothing would prevent Oz from remaining dormant within Jack's body. Instead, Oz manages to use his powers to destroy what's left of Jack's soul.
Following this, Oscar helps Oz, Gil and Alice (who had returned to Oz after Oz called her soul back to him) reach St. Luca's Gate, opening it with his Key to the Abyss (his wedding ring), and telling the three of them to leave without him, as St. Luca's Gate would lead them out of Reveil safely. Oscar closed St. Luca's Gate with his Key, speaking with Xai as he confronted Oscar. Xai shoots and kills Oscar for allowing Oz, Alice and Gilbert to escape, having originally planned on stealing Oscar's Key; however because St. Luca's Gate had been closed, Xai could not use the Key to open it for some time due to the effect of the Gate.