When demons begin appearing on Earth unpredictably, foreshadowing a cataclysmic breakdown of their magic, Artemis and his friends face a new foe--a twelve-year-old girl whose intellect just might match Artemis's own--as they try to prevent catastrophe.

Artemis's mother has contracted a deadly disease -- and the only cure lies in the brain fluid of African lemurs. Unfortunately, Artemis himself was responsible for making the lemurs extinct five years ago. Now he must enlist the aid of his fairy friends to travel back in time and save them. Not only that, but he must face his deadliest foe yet...his younger self. When the only way to save his mother's life lies with the lemurs he made extinct years...

Told in alternating voices, twelve-year-old Sami, from a village along the Bay of Bengal, and fourteen-year-old Yuki, from Northern Canada, strive to protect their homes from the encroaching damage brought on by climate change. "From New York Times bestselling author Eoin Colfer and the team behind the Artemis Fowl graphic novels and bestselling, acclaimed graphic novel Illegal comes a compelling and timely story that follows two courageous children...