The Decision (Animorphs #18)

Ax and the Animorphs face a perilous situation after morphing into mosquitoes to evade the Yeerks, leading them to become stranded in Zero-space with no way back to Earth and limited oxygen. An Andalite scout ship discovers them just in time, offering rescue and a new connection for Ax with his own people. The story explores themes of belonging and the uncertainty of returning home.