The following version of this book was used to create the guide: Doerr, Anthony. Cloud Cuckoo Land. Scribner, 2021.

Anthony Doerr's novel Cloud Cuckoo Land is divided into 24 numbered and titled sections. These structural divisions are inspired by the 24 remaining folios of Antonius Diogenes's antiquated tale, Cloud Cuckoo Land, a fictional text integral to Doerr’s plot. Each of Doerr's sections presents a new fragment from Diogenes's story, and is then divided into another series of narrative subsections. These subsections trace the lives and experiences of five main characters: Konstance, Zeno, Seymour, Anna, and Omeir. Though the characters all live in different places or eras, they are all connected by Diogenes's book.

The following summary employs the present tense, and adheres to a linear mode of explanation.

In the mid-1400s, a young orphan named Anna lives in Constantinople. Because she has no parents and no money, she is consigned to a life working for an embroidery house. She finds little joy in the work, despite her sister Maria's embroidery talent. Anna uses her imagination to escape the confines of her reality. One day, Anna overhears an old man, Licinius, teaching a group of boys the story of Ulysses. She convinces Licinius to give her lessons in exchange for wine. On the day of their last lesson, Licinius gifts Anna his scrolls.

One night at the embroidery house, Anna's master discovers the scrolls and blames Maria. He punishes her by beating her head on the stone. Maria suffers health repercussions. Feeling guilty, Anna tries making money to pay for Maria's healing. While selling stolen chickens, she meets a boy, Himerius, who says if she helps him climb into the abandoned priory, they can sell the valuables inside for more money. Anna agrees. Inside the priory, she discovers a wealth of ancient texts, which she and Himerius sell to Italian scribes. These ventures open Anna to new worlds.

Meanwhile, the new sultan's army creeps closer to Constantinople. The inhabitants begin to flee. The scribes disappear. Himerius leaves. Maria dies. Anna feels alone. Finally she takes her one remaining book, and sneaks out of the city.

Just miles away, Omeir is camped outside the Constantinople walls with the sultan's men. Though Omeir is still a young boy, Omeir has been forced into the sultan's service. As a child, everyone believed Omeir’s hairlip was a sign of demon possession. Omeir, therefore, learned to relate to animals more than humans. He and his oxen, Moonlight and Tree, have been constant companions. When the sultan's mission proves abusive and destructive, Omeir fears for his oxen's life. They soon die while trying to build the sultan's cannon. Once the cannon is finished, Omeir heads for home. On his way, he meets Anna. Together they journey back to the ravine, where they create a life together. Through Anna, Omeir learns about Diogenes’s tale. Years later, when Omeir is an old man, he brings the book to Italian scribes for posterity.

Zeno grows up in Lakeport, Idaho with his father during the 1940s. Because Zeno is marginalized by the other children, he learns to find comfort in books. Then, in 1941, the country goes to war and Zeno's father enlists. Zeno moves in with his father's girlfriend, Mrs. Boydstrun. Not long later, they receive word that Zeno's father has died.

When Zeno is 17, he enlists and is deployed to Korea. He feels happy to leave Lakeport. Not long later, he is attacked and imprisoned by a band of Chinese soldiers. While at the prisoner of war camp, Zeno meets a British soldier named Rex. He becomes closer to Rex than he has ever been with anyone. Yet when Rex makes a plan for them to escape together, Zeno fails to follow through.

Years after returning to the States, Zeno tries to find Rex. Finally Rex sends him a letter, inviting him to London. Zeno accepts the invitation, but is disappointed to discover that Rex is already involved with another man. When he goes home to Lakeport, he returns to his former translation endeavors. He soon learns about a recently discovered Greek manuscript: Antonius Diogenes's Cloud Cuckoo Land. Zeno spends months translating the text. Eventually he works with five fifth graders to convert the story to the stage.

On the night of the children's dress rehearsal, Zeno hears gunshots on the ground floor of the library. When he learns what is happening, he sacrifices his life to save the children.

Lakeport teenager, Seymour, attempts to bomb the Lakeport Public Library. After a local realty company destroyed the woodlands behind his house, Seymour became desperate for vengeance. By placing the bomb in the library, he thinks he can hit the neighboring realty building. The children's librarian stops him while he is placing the bombs, and Seymour shoots him.

Seymour sits in the library waiting for deliverance. Ultimately, he is arrested and tried. While in prison, he is given a work assignment with the company, Ilium. Through Ilium, Seymour works on creating a comprehensive digital map of Earth. Disturbed that the company wants him to whitewash the imagery, Seymour hides complex codes in the software that interrogative users might use to uncover the truth beneath.

Many years later, Konstance is living on the Argos, a spaceship bound for the new planet Beta Oph2. When a virus sweeps the ship, locking Konstance in a vault, and killing everyone else on board, Konstance begins to question her understanding of reality. The more questions she asks the ship's operating computer, Sybil, the fewer answers she uncovers. She uses the ship's library and Atlas program to discover the truth. Eventually Konstance realizes that the Argos is not in space and has never left Earth. She breaks out of the vault and through the ship walls. Outside she discovers that, contrary to the Argos inhabitants’ belief, life on Earth still exists. She eventually finds other humans and starts a new life, within which her reconstructed fragments of Diogenes's tale remain a constant comfort.