A young girl must battle an evil force threatening the planet Althea's healing powers while fighting for her own life.

A bubbly eighth grader's life is transformed when she receives a diagnosis of leukemia. Something about Liv Silverstein's illness makes the typical treatments ineffective, and her doctors recommend an unorthodox path forward. The only way to save Liv's life is to transport her to the planet of healing, Althea. Desperate, Liv's parents agree and Liv is whisked off by flying horses to a planet they never knew existed.

At first, Althea seems to be the realization of Liv's childhood fantasies. Gifted with a wisecracking cat named Monticelli, Liv makes friends with mermaids and a half-elf boy, Caleb. When a mermaid becomes ill, Altheans realize their planet is suffering. A destructive purple mist washes over the land, polluting the water. Butterflies and plants are dying, and without its plants, Althea cannot heal the mermaid-or Liv.

Under the guidance of a wise elder named Dara, a reluctant Liv sets out to defend Althea, with the help of Monticelli and Caleb. After a challenging journey, they meet Emelina, a young girl possessed by the spirit of the evil Hadeon. Increasingly weakened by her untreated condition, Liv's stamina threatens to expose the group to Emelina/Hadeon's powers.

How will the trio, led by the fearless yet ailing Liv, survive this journey, defeat Hadeon, save Althea, and save Liv along the way?