There is a kind of book a seasoned writer produces after a big success: large-hearted, wide in scope and joyous. Following his Pulitzer winner All the Light We Cannot See, Anthony Doerr’s Cloud Cuckoo Land is a deep lungful of fresh air – and a gift of a novel. The story crystallises around a book within a book, the existence of which is imagined by Doerr, though its author is a real writer of the ancient world. Antonius Diogenes’ Cloud Cuckoo Land is a fabulous adventure story written by Diogenes for his niece, to beguile and console her during an illness. It tells of a shepherd, Aethon, known by his neighbours as “a dull-witted mutton-headed lamebrain”. Aethon longs to travel to a rumoured paradise, a city in the sky populated by birds. To get to the city and enter it, Aethon must be a bird and not a human, since humans are wreckers and ruiners expressly banned from this wonderful utopia. By various mishaps and trickery, Aethon has to spend time as a donkey and a fish – a mistreated domestic beast of burden and a wandering, then trapped, wild animal.

It is clear from the opening chapters of Doerr’s Cloud Cuckoo Land that the novel’s characters, in their different time periods, will have something to do with this book inside a book, whether as champion, custodian or threat. One of the joys for the reader is in figuring out when Diogenes’s book will appear and what purpose it will serve Anna, Omeir, Zeno, Seymour and Konstance: what trouble it might cause or blessing it might bestow.

Young Anna, in 15th-century Constantinople, is an orphan with a sick sister; they spend their lives doing needlework for the church. Anna may be bad at embroidery, but she has an illicit skill: someone has taught her to read. Omeir is a boy with a cleft lip living on a farm with his mother, sisters, grandfather and his two beloved oxen, Moonlight and Tree. Oxen and ox driver are dragooned by the sultan’s great army, which is on its way to lay siege to Constantinople. Then, half a millennium later, there is Zeno Ninis of Lakeport, Idaho, a veteran of the Korean war whose emotional life is a casualty of mid-century midwestern bigotry.

In Korea, Zeno learned ancient Greek from a fellow prisoner of war, a man who is later the author of a Compendium of Lost Books. Late in Zeno’s life, when one of those lost books – you can guess which one – is discovered, he sets out to translate it. In 2020, he is working with local children, putting on a play based on the book. But at the dress rehearsal in the public library, they are under threat from Seymour, the novel’s most worrying, touching and tenderly handled character – an angry young man who was a broken-hearted boy, a faithful soul easily beguiled by the forces of malice that lurk online. Lastly there is Konstance, whom we meet at ages 10 to 14 on the giant exo-ship Argos, in the 65th year of its voyage of escape from a ruined Earth. Konstance spends a lot of time in the ship’s library – a library that exists digitally inside the vessel’s godlike AI, Sybil.

These are the characters of the book, both humans and machine. The shepherd Aethon’s difficulties as donkey and fish, meanwhile, mirror the precarious lives of the animal characters: the twin oxen, Tree and Moonlight, and the godlike Trustyfriend, a great grey owl, whose existence quiets the mind of noise-besieged, autistic Seymour. Each character’s story is graceful and suspenseful in itself, but it is the deftness, cunning and feeling with which the author braids them around the tale of the dim-witted lamebrain who longs to be a bird that make this book the simultaneously risky and necessary wonder it is.

Diogenes’s Cloud Cuckoo Land is the thread the reader follows into and out of this labyrinth. Diogenes tells his niece he has transcribed the tale from tablets found in a grave: that it is not invented, but something found in the world, like so many things in this novel. At the earliest date in the book – 1439 – it survives in one copy in a ruined library, from where it is stolen or possibly rescued. Later it is carried away from a sacked city and hidden in a hollow tree. Next it is deposited in a famous library, forgotten, and much later recorded as lost. This means that when it is found again it becomes an enormously exciting object, reproduced in facsimile and distributed digitally. Zeno turns the story into a play with the assistance of the children who will perform it; still later, it is reassembled from that script, printed, digitised again. This copy is hidden, like a secret item in a computer game, where it waits for the person who will need it in order to do more than just get to the end of the game. All along its journey and throughout its changes, Diogenes’s book is read to young people and sick people, and those recovering from wounds to their souls. The reading and sharing is always an act of love.

Doerr’s Cloud Cuckoo Land argues that love, care and putting things back together are the best uses of human energy. Yet this is a novel in which work isn’t just a costume its characters are wearing over their emotional lives. We see tedious, dangerous and undervalued occupations, but also share the fever of ingenuity in the making of a fortress-smashing 15th-century cannon, marvelling along with a whole army at the process and the result. We see the shrewdness of the twin oxen pulling together, understanding each other, with the invisible results that come when work goes right and the cart doesn’t fall into a ravine, or when only one wheel goes into the mud.

This is a novel so full that, if it can be said to be “about” anything, perhaps it is about how things survive by chance, and through love. But the book is also keenly aware of the fact that humans have basically exhausted our chances, and it is time for a fierce and tenacious love to step up – by sharing and passing on what is mended and changed, like Diogenes’s book, with its delights and consolations – to save what we still have on Earth, and what is ours, as well as what we enjoy here, though it isn’t ours.

Diogenes’s little fable, when we last see it, has been carried off again by a loving custodian. But what happens to Sybil, the single-minded AI of the exo-ship Argos, and the great library she contains? The end of the novel is hopeful, but it still seems to have a question built into it: civilisation or the natural world? For this reader, it was what happened to the novel’s final library that made her look up from the page and the world of the book to think hard about our world, and that question. With all its tenderness for human life and animal life, and libraries, this novel nevertheless acknowledges that civilisation continues to insist on not going anywhere without packing its poisons.

• Elizabeth Knox’s The Absolute Book is published by Michael Joseph. Cloud Cuckoo Land by Anthony Doerr is published by 4th Estate (£20). To support the Guardian and the Observer by a copy at guardianbookshop.com. Delivery charges may apply.

• This review was amended on December 13 2021 to correct the setting of Lakeport, Idaho.