The Forgotten

The Animorphs have met the Ellimist, a being from another plane of existence, who helps in their fight against the Yeerks, but they are still unsure if he is a friend or foe. In the next adventure, Jake, the leader of the Animorphs, accidentally falls through a dimensional rift and lands on a version of Earth where the Yeerks have won. With help from Ax and the others, Jake tries to get back to his own dimension.