The Plains of Passage is the fourth book in Jean M. Auel’s Earth's Children series, set during prehistoric times. The novel follows the journey of Ayla and her partner, Jondalar, as they travel across Ice Age Europe. Their goal is to return to Jondalar’s people, the Zelandonii, but the journey is perilous. Along the way, they face numerous challenges, including dangerous landscapes, harsh climates, and encounters with various tribes. Throughout their travels, Ayla’s skills as a healer and her ability to communicate with animals are highlighted. The novel emphasizes survival, relationships, and the cultural practices of prehistoric tribes.