Cassie and her Animorph companions meet a treacherous new enemy, the Helmacrons, tiny but unexpectedly lethal invaders who have the ability to shrink others to their size and who are taking hostages to recover their spaceship.

When David's girlfriend Senna is swallowed up by the Earth, he and his friends follow to save her, only to stumble upon a nightmarish land they could have never imagined.

Christopher and his companions manage to escape from Fairy Land only to land in Olympus, the section of Everworld where the ancient Greek gods live, which is about to become the latest target of the insect-like forces of Ka Anor, the god who consumes other gods.

"Byx is the youngest member of her dairne pack. Believed to possess remarkable abilities, her mythical doglike species has been hunted to near extinction in the war-torn kingdom of Nedarra. After her pack is hunted down and killed, Byx fears she may be the last of her species. The Endling. So Byx sets out to find safe haven, and to see if the legends of other hidden dairnes are true. Along the way, she meets new allies--animals and humans alike--who...