The Hidden
K. A. Applegate
 The Yeerks repair a downed Helmacron ship and use its sensors to track the Escafil Device and the Animorphs morphing abilities. Cassie is forced to relocate the Escafil Device. During the process, a Cape buffalo and an ant inadvertently gain the morphing ability. The buffalo morphs Chapman and begins to learn speech, and the ant morphs Cassie. Cassie kills the ant when it demorphs, and near the end of the book the buffalo is killed by a Dracon beam. However, the Animorphs come up with a plan similar to Megamorphs #1, in which Cassie morphs a humpback whale in midair to destroy the helicopter carrying the Helmacron ship.