Volume Four of Chrono Crusade begins with Rosette talking on the phone with Sister Kate, who is less than pleased about the trouble Rosette keeps getting into. (Meanwhile, Satella is extremely smug about being a rich, self-employed bounty hunter.) After some more squabbling between Rosette and Satella, Rosette goes to check on Chrono, who is having Symbolic Nightmares of Doom. (We see that Chrono has some very deep issues that have yet to be resolved, most of them centered around Aion.)
The next segment is one long car chase involving two “Pursuers” who have found Chrono’s trail. During the car chase, the Pursuers helpfully provide some exposition about why there is a price on Chrono’s head. After losing the demons, Rosette and company hole up in some kind of warehouse, where Chrono fills everyone in on the situation with the Pursuers. From there, it is decided that Chrono should give even more exposition on why demons are calling him a “Sinner.”
Then we segue to Fiore and Aion back at the beach house. There is an eerily domestic scene between Aion and Fiore where Aion seems more like a slightly dorky sweetheart instead of an Evil Antagonist. (He can apparently turn the Evil Overlord Act on and off at will.) Aion learns from Fiore and Rizelle’s remaining spider about what happened on the train. Aion’s general demeanor during this is somewhat exasperated, but his mood brightens noticeably when he realizes that one of the “Apostles” he’d been looking for has been found. (That would be Azmaria.)
While Aion is learning that Chrono has Azmaria, Chrono is back at the warehouse telling the story of Why There is a Price on His Head. They are waiting for back up from the Chicago branch of the order, but the Pursuers arrive first. A battle ensues with the Pursuers, with the operatives from the Chicago branch and Father Remington arriving to mop up the mess. Rosette and company get hustled off onto the next stage of their journey while Remington questions the remaining Pursuer. (It is revealed at this point that there has been some kind of exodus from Pandaemonium occurring, resulting in an “invasion” of demonic refugees.) Since Rosette has pretty much proven to be slightly incompetent when it comes to cross-country travel, Rosette and friends get bundled onto a plane to San Francisco. Fortunately, the plane does not crash.
We cut back to Aion, who is telling the other Sinners that the “Songstress of Vegas” will be arriving soon, the in the company of Rosette and Chrono. He also lets slip that Rizelle is dead, which greatly upsets Genai. Next is an altercation where Genai wants to beat up or kill Joshua, but he is prevented from doing this by Aion and Fiore. (We learn that Genai blames Joshua because Joshua was apparently the one who sent Rizelle. This is very interesting because it is apparent that Aion has given the kid considerable authority, which Genai and apparently Rizelle greatly resented.) We get a few more hints of what Aion might be up to, and then we switch back to Rosette and friends.
The volume ends with Rosette and friends arriving in San Francisco. Since they are underfoot and somewhat in the way, they are shooed off to a carnival but the older members of the Order who are attempting to make the San Francisco headquarters livable. (The Order does not have many people on the west coast, which is probably a major reason why Aion’s group is in California.) Everyone has fun at the carnival, and Rosette and Chrono have a heart to heart conversation which is interrupted by Aion’s pet eagle. The very last scene is a confrontation between Rosette and Joshua. (Cue ominous music in the background.)