The Book of Thel introduces us to a virginal shepherdess girl named Thel, who resides in the Vales of Har along with her mother and sisters. Thel is a loner who is experiencing something of an existential crisis in that she doesn't understand why all beings must eventually grow old and die.

Thel wanders the countryside and meets the Lily of the Valley and the Cloud, both of whom try to comfort her, but Thel remains inconsolable. The Cloud, in particular, seeks to assuage some of Thel's fears by saying that although he is sometimes not visible, he is always present. Thel counters that it is not the same for her, because when she dies, she will only be "food for worms." The cloud encourages her to think differently about her time on earth, because humans should not live only for themselves.

Thel continues her journey and meets a Clod of Clay, who encourages her to visit her realm beneath the ground where Thel—and all the dead—will eventually reside. The Clod of Clay can be seen as a symbol for Jesus' becoming human (transforming into a man of clay, like Adam). Thel cautiously enters the Clod of Clay's dominion, a "land of sorrows and of tears," but then becomes aware of plaintive, impossibly sad voices that cause her great distress. Thel cannot bear to stay any longer and flees home, unable or unwilling to believe that we have so little control over our own destiny. Thel remains an eternal, innocent virgin, because she cannot contemplate a future devoid of her own existence.