Plot summary
In the form of a phoenix, Tess flies out of her room to join Kevin, who is now permanently in the shape of such a magical bird. She tries to ask Kevin what has happened to him since they last spoke, but her mind is overwhelmed by the purity and beauty of the phoenix's nature, and she instantly loses interest in asking questions. The following night, she becomes worried about the restless behaviour of her pet rat Algernon, and her animal-mind detects a telepathic summons being sent to all the rats in the city. Algernon breaks out of his cage and escapes into the sewers, and as a rat Tess follows him to an empty house filled with thousands of his kind. There, she discovers that the source of the mysterious call is a male Switcher. The next day, Tess investigates the house, and sees a red haired boy standing in the doorway of a house across the street. Somehow sensing that he is the Switcher, she resolves to speak to him when she gets the chance.
Upon reading a newspaper article, Tess discovers that the phoenix has been captured in the Phoenix Park, and is now on display in Dublin Zoo. Therefore, she sets off to visit the Switcher and ask for help in breaking her friend out of confinement. Tess finds the boy (Martin) sleeping in the darkness of his room, and tells him that she knows he is a Switcher. Martin agrees to help her, but only on the condition that she return to his house that night so that he can demonstrate his skill as a Switcher to her. When she does return, he takes her for a walk through the streets, and then demonstrates the truly awesome and horrible skill which he has learned by Switching into a vampire. Martin feeds on her blood, the shock of which stimulates Tess' survival instincts, and she Switches into the only form in which she will be safe from Martin: a vampire. Once she is in this form, all of Tess' revulsion toward the concept of vampirism vanishes, but Martin warns her not to kill her victim when she feeds, as doing so would arouse suspicion. After much hunting, the two come upon a young couple in a car, on whose blood they feed.
For the next few days, Tess behaves scornfully toward her parents, upsetting them greatly. At last when her mother mentions the phoenix, the memory of her time as one of those glorious, pure bird dispels the lingering aspects of the vampire personality, and she apologises for her behaviour. The family visit the zoo to see the bird, and there Tess meets Lizzie, who claims to be worried about something. The old woman informs her that the phoenix is a powerful force of good, and will change many lives, but according to the nature of the world, some dark force must have come into existence to balance out the presence of the phoenix. Upon entering the building in which the bird is caged, Tess is suddenly overcome by a feeling of joy and warmth, and realises that the bird is having this effect on everyone who sees it. Outside, she and her parents enjoy a game of Frisbee, all their arguments forgotten, not even becoming upset when Tess accidentally loses the Frisbee in the bushes. However, Lizzie tells Tess that she has "work to do", and is wasting time.
Tess visits Martin again, and he explains to her the gruesome circumstances of his father's death. She is horrified, but he seems not to care. He takes her into the crypt which he plans to make his home, and she realises that he has been using the rats to excavate this crypt. She tells him that she never wants to return to being a vampire, but Martin claims that now he has bitten her, she will become one of the undead as soon as she dies. He tells her that his fifteenth birthday is the following day, and, because he intends to remain a vampire, he offers her the chance to join him willingly. She refuses, claiming that if she chooses to become an immortal phoenix, she will never succumb to death or vampirism. So as to destroy Tess' confidence, Martin sends the city's rats to kill Kevin at the zoo, but the phoenix escapes with Tess's help. He and Martin confront each other in the park, and Tess steps between them, where she is confronted with the choice between becoming like either of them. Martin uses his hypnotic powers to coerce her, and in turn Kevin uses his purifying powers to draw her toward him. Tess alternates between allegiances and the struggle within her becomes so strong that it begins to damage her mind. As she tries desperately to choose her path, Tess suddenly remembers some prior advice given by Lizzie, and realises what she is doing wrong: She has been convinced that she must choose to be either a vampire or a phoenix, when in fact, the option of simply remaining human was never closed to her. Tess chooses to retain her humanity, and this somehow transforms both Martin and Kevin back into their human forms. Martin, his defences lowered, breaks down over the loss of his father, but when Tess tries to comfort him, he realises he is vulnerable and runs off into the trees. Tess follows, but slips on the Frisbee which she lost earlier.
Tess enters Martin's home in the form of a cat, and but doesn't see Martin there. She checks on Martin's mother, on whom Tess has realised that Martin had been feeding for a while before she met him. However it seems that his mother is still alive, though exhausted. Tess takes Kevin back to her home, where they discuss the events of the past few days. Kevin claims that because he and Martin balanced each other out, Martin's return to humanity meant that Kevin too lost his supernatural form. Their discussion is interrupted by the arrival of Algernon, who informs them that Martin has disappeared, and that his control over the rats of the city is broken. Tess and Kevin realise that Martin has chosen to remain human, and decide to help him through his newly exposed grief.
