The Unknown (Animorphs #14)

In this thrilling installment, a rumor circulates about a hidden item at the secretive Zone 91 that reportedly proves the existence of extraterrestrial life. The Animorphs, already familiar with alien threats, realize that their enemies, the Yeerks, are eager to uncover this mystery to further their plan of domination on Earth. Determined to protect their planet, the Animorphs embark on a daring mission to Zone 91, only to face unexpected revelations that challenge everything they know.