Face Off (1) (S01E19)

The Animorphs face a terrifying new threat: Yeerks that can survive without Kandrona rays. These rogue parasites no longer need to return to the pool ship, making them impossible to track or starve out. Jake and the team realize their usual tactics are useless against an enemy that can stay in a host indefinitely. As the Yeerks begin seizing more powerful Controllers, the Animorphs must race to find a weakness before their own families and friends become permanent prisoners.