A Tale of Phoenix by Sandra Hayes
Phoenix, though entirely blameless, carries the guilt of his twin sister's death at birth and feels as though he is cursed. Events seem to confirm this when a family death occurs on each of his leap-year birthdays.
On his twelfth birthday, Phoenixs bad luck accumulates in a near death experience, when he is caught in a fire. Whilst lying in a coma in this life, in another world - on an island called Lila - his story unfolds. Here, he meets Maya, his twin sister, who becomes his guide across the island. The whole island however seems to be under a curse and Phoenix finds himself in difficult situations; he escapes a heart-hunting beast, rescues a little boy called Karun from his death and tries to bring him to safety.
During his journey Phoenix finds a storybook about Lila, where a mermaid called Marina seems to want to help him. Soon, the two worlds intersect and Marina guides Phoenix deeper into the heart of the island, where he must save Karun and awaken himself from his coma and try to return to the real world alive.