The Immortal Fire was adapted into an audiobook in 2013 and is narrated by Cassandra Morris.

The Immortal Fire is the final book in the trilogy.

 It is preceded by The Siren Song and earlier, The Shadow Thieves.

As the third and final book in Ursu’s trilogy The Cronus Chronicles begins, Charlotte Mielswetski is recovering from the injuries that she sustained following her battle against Philonecron (a primary antagonist across the previous two novels) and his grandfather, Poseidon – the Greek God of the sea, earthquakes, and horses. In an attempt to avenge his demotion from the Underworld, and the loss of his immortality, Philonecron targets both Charlotte and her cousin Zee for preventing his overthrow of Hades in the first novel, leading to their battle on Poseidon’s yacht as well as another cruise ship; the Isis Queen whose cruise was designed to lure Charlotte to Philonecron and Poseidon in the middle of the Mediterranean.

Here, Charlotte defeats Philonecron who in the epilogue of the second novel is swallowed by the mythical monster, the Ketos. However, unbeknownst to both Charlotte and Zee, Philonecron comes into possession of Poseidon’s powerful trident, a detail mentioned in the prologue of the third novel and setting up the series of strange events that begins the novel. 

In the days after the battle, Charlotte learns that all the sea life within a mile radius of the ill-fated shipwreck located in the middle of the Mediterranean has disappeared. Sensing a pattern, Charlotte connects the disappearance of the sea-life to a host of other phenomena such as increasing whirlpools, parts of the ocean turning black as well as the disappearance of several people that are suspiciously replaced by stone replicas. These events are the work of her nemesis, Philonecron, whose possession of Poseidon’s trident equips him with the ability to destroy Charlotte and Zee and challenge Zeus as the head of Olympus. 

Meanwhile, a chimera attacks Charlotte at her high school. She is rescued by Zee and their teacher/mentor, Mr Metos. Mr. Metos suspects that the remainder of the Olympians are threatened by Charlotte and Zee (as the last to see Poseidon before his disappearance). Mr. Metos introduces Charlotte and Zee to the Prometheans, a group of living descendants tracing their ancestry back to the Titan Prometheus, whose aim is to protect mortals such as Charlotte and Zee.  

While en route to the Prometheans’ Lair in London, Charlotte is plagued by dreams of being in a cave room lit only by a small but intense fire that illuminated strange markings on the wall. In this dream, Charlotte hears the voice of a girl encouraging her to understand the images on the wall, but uncertain, Charlotte wakes up after the girl becomes exasperated by her lack of knowledge about what the markings mean. Zee, it is also revealed is experiencing strange dreams to “seek the belly-button” (a clue later revealed to be pushing Charlotte and Zee to Delphi). These dreams progressively become more frequent and eventually the cousins realise that the mysterious girl, recurring from the second novel where she warned Zee about Charlotte’s cruise; is guiding Charlotte and Zee to find Prometheus’ flame and use it against Zeus. 

While at the Lair, Charlotte and Zee discover that the Prometheans have a ruthless moral code in ensuring the protection of mortals: it is revealed that a boy in the cupboard, Steve (later revealed to be one of Zeus’ many sons) is “worth a great deal” as a sacrifice to stop the conflict (p. 256). Charlotte and Zee decide they can however no longer sit idle and be complicit in a manner of fighting they do not agree with: they break out of the headquarters with Steve in tow, aiming to go to Delphi, Greece (the “belly-button” of the world) and from there to Olympus. 

While escaping, Charlotte and Zee are separated from Steve, who is intercepted by Philonecron (in disguise as a man named Phil Onacron), who encourages Steve to find his absent father, Zeus, and confront him.  Meanwhile Charlotte and Zee get help from their friend Sir Laurence, a wealthy gentleman they had helped in the previous novel: he charters a private flight to Delphi so that they can retrieve the Promethean Flame.  There, they enter the Temple of Apollo, overcome its defenses, and capture the flame.   

Equipped with their weapon to destroy Olympus, Charlotte and Zee then go to Museum of Delphi to find the omphalos (the so-called ‘belly-button” of Delphi) which Zee suspects is the entryway to confronting the Olympians. They then become separated by a cloud nymph who insists their journeys “must be made alone”(p. 345). To prove her worth, Charlotte is first transported to a scene from Middle School before being confronted with the Sphinx guarding her doorway to the next part of Olympus. For Charlotte to progress, she must justify whether humanity deserves to be saved but she is interrupted when Mew, the cat (revealed to be Zee’s grandmother reincarnated) fights the Sphinx to distract it. This allows Charlotte the time to get through the door and continue on her way. Finding herself in the reception of Mount Olympus, Charlotte takes the nearest elevator but after an uncomfortable exchange with Ares, the God of War, she eventually makes her way into a room with five other Olympians. Hiding, she listens to their conversations about her and Zee and fails to notice that she has been pierced with one of Cupid’s arrows.

Meanwhile, Zee arrives at another entry to Olympus and is distraught without his cousin. Distracted by Charlotte’s absence,  Zee almost sees Artemis but is then pulled away by a satyr who then tasks Zee with walking through a forest to meet Hecate at the entry to Olympus. Along the way the satyr and Zee talk about who might be trying to harm Charlotte, which leads to the revelation that Philonecron is not only alive, but he has made his way to Olympus. Urging them to go and find Charlotte, Zee is tricked into carrying the backpack and rocks that the Satyr previously held. Before fleeing, he remarks that these rocks are now Zee’s burden and to relieve himself of their weight he must give them to another. After being left by the Satyr, Zee eventually arrives at a series of crossroads and sees a hallucination of Charlotte which he realises is not real. This breaks the imaginary quest, leading Zee to be returned to the staircase up to Olympus. Here he is confronted by the girl from his dreams, who demands he tell her where the flame is (it is in a lighter, which Zee is holding).

Zee refuses to go any further before knowing why he has been tasked with finding and now, using the flame. The girl remarks that it is so people will again have knowledge of the gods and this will annoy the gods, especially Zeus as they can longer ignore the mortals as they had previously done for centuries. Zee concludes that the girl is only motivated by revenge and not justice like he initially thought. She ultimately reveals herself (via transformation) to be Persephone, the daughter of Zeus who has been a minor character from the first novel and has been shown to have been helping Charlotte and Zee as well as perform her own tasks, independent of her role as the Queen of the Underworld. 

It is then revealed that Prometheus tasked Persephone with finding a mortal to use the flame against the Olympians. Zee however realises that this is not their own quest but that the flame is being used to serve the selfish desires of the gods, included Persephone whose actions to this point (such as warning Zee about the cruise ship in the second novel, but putting Charlotte’s life at risk to motivate Zee) are similarly self-motivated. He therefore refuses to use the flame and because of this Persephone disappears before the other deities can realise she is behind the rediscovery of the flame. Before Zee can wonder where Persephone has disappeared to, he is transported to the throne room and confronted by Zeus about the lighter and as he goes to touch it, it causes Zeus immense pain. 

The separate plotlines converge when both Charlotte and Zee see one another within Zeus’ chamber. Charlotte, who has been healed by Apollo, has been brought up to the room by Hera.  initially fails to see her cousin due the brightness of the room. However, Zee immediately sees Charlotte, blood-soaked clothing, and all. The two struggle to get back up and then try to persuade Zeus to not destroy humanity which leads Zee to offer himself up as a sacrifice to save the rest of humanity- the discussion of which leads Zeus to use his thunderbolt and attack Charlotte. Despite being puzzled by Zee’s offer, Zeus rejects this and instead swears by the river Styx that if Charlotte is sacrificed, he will not harm any of humanity. Unbeknownst to both Zee and Zeus, Charlotte has overheard the conversation and willingly sacrifices herself by rolling off the edge of Olympus. 

Believing Charlotte to be dead, Zee is devastated but convinces Zeus that he must uphold his promise to not destroy humanity as he never specified that Zee had to make the choice for Charlotte to sacrifice herself. In the meantime, as Charlotte hurtles towards the underworld, she is saved by Persephone, in the guise of a large bird. Persephone insists she must take Charlotte back to Olympus as it is the right thing to do and in thanks for Charlotte’s protection of the dead during her time in the Underworld in the first novel. Persephone also insists that Charlotte must return in order to prevent Philonecron who now has Steve to use the trident, from defeating Zeus. 

Philonecron and Steve force their way to Zeus’ chamber and immediately restrain Zeus. Despite the shock of losing Charlotte, and seeing Philonecron in the flesh again, Zee realises that he must focus his attention on Steve, whose anger will only be used by Philonecron and his own ambitions. After reminding Steve of Charlotte’s sacrifice and what she would want Steve to do, Steve yells at Philonecron that he does not “have to do anything I don’t want to do” (p. 490) and that he now realises he does not have to be angry at Zeus as he simply a “pathetic coward” (p. 490) not worthy of his emotions. 

Following Steve’s decision, the tension in the plot quickly dissipates as Philonecron, trying to control Zee is forced to the edge of Olympus and picked up by the Persephone-as-a-bird who then flies off with the half demon. Released from his restraints, Zeus then insists that Charlotte and Zee then destroy the flame, which they do but not before getting Zeus to swear on the river Styx that he will not harm them or humanity again. Shortly thereafter, Persephone reunites with Charlotte and Zee and  directs the children off Olympus and back to Greece before returning back to the U.S. alongside Sir Laurence and Mr. Metos, having saved humanity.

As the final book in her Cronus Chronicles trilogy, Ursu’s The Immortal Fire marks the end of Charlotte and Zee’s adventures with the divine world. It offers a substantive reception of Ancient Greek mythology through references that align the mythical and modern world.

This is achieved through a combination of  direct and indirect receptions. The most significant of these inclusions involve include the appearance of Steve, one of Zeus’ children who is angered both by not having a father and by seeing his mother upset at Zeus’ abandonment. Steve’s arc plays an integral role in the narrative as he is befriended (and persuaded) by Philonecron who manipulates Steve into wanting to harm Zeus. Through Steve, Ursu addresses quintessential emotions and questions around identity, abandonment, anger, and loss by reshaping Zeus into a figure whose mythic past (addressed flippantly in this text) renders him pathetic and concurrently recognisable to readers as a character who at once is the King of the Gods but also all too human with regards to his poor decision making. 

Ursu further establishes how the Greek Pantheon’s significance has reduced over time, emphasizing the Olympians’ fickleness. Perpetuating a tradition that stems from antiquity, the gods here are adjusted to be represented as petty and at times, pathetic. Even Persephone (normally presented as a figure on the side of right), who is framed as a morally ambiguous character and often supporting both Charlotte and Zee acknowledge that she has treated them poorly in her own desire to take revenge against Zeus and the other Olympians. In direct contrast to this Persephone’s characterisation, Charlotte and Zee are framed as the moral centre of the text. Their actions resonate with Ursu’s readership who are beginning to find their own identities and question the views, values and beliefs of those around them, especially authority figures. In doing so, Charlotte and Zee’s exploration of the difference between revenge and justice, as well as their interaction with the Olympian deities before making up their own decisions acts as a source of inspiration for readers uncertain about the value of their own voice. 

Additionally, those characters who engage in poor or selfish decision-making are predominantly Olympian deities. It is their limited perspective or outdated views that make figures like Hera, Aphrodite and Apollo reluctant to help prevent Philonecron’s rebellion.  Similarly, characters like Mr. Metos and Timon, descendants of the Prometheans, rationalise the use of Steve, a mortal (and innocent) boy as leverage/sacrifice to prevent Zeus destroying humanity. In these instances, both Charlotte and Zee reject these positions and are instead determined to find other ways, including relying on themselves, to resolve their problems.

Thus, by diminishing the glamour associated with the Greek Pantheon and showing her child protagonists achieving their goals, Ursu encourages a sense of empowerment in her young audience.

Brown, Sarah Annes, “The Classical Pantheon in Children’s Fantasy Literature” in Brett M. Rogers and Benjamin Eldon Stevens, eds., Classical Traditions in Modern Fantasy, Oxford: Oxford University Press, 2017, 189–209.

Castleman, Michele, Meeting Gods: The re-presentation and inclusion of figures of myth in early twenty-first-century young adult and middle-grade children's novels, Ohio State University, Doctoral dissertation, 2011.