In Green's Jungles is the second volume, after On Blue's Waters, of Wolfe's ambitious SF trilogy, The Book of the Short Sun. This book is narrated by Horn, who was also the narrator of the first volume and now has embarked on a quest from his home on the planet Blue in search of the heroic leader Patera Silk.
As Horn's quest somehow continues to move both backward and forward, he recalls visiting the Whorl, an enormous spacecraft that brought settlers from Urth, and going thence to the planet Green, home of the blood-drinking alien inhumi. There, he led a band of mercenary soldiers, answered to the name of Rajan, and later became the ruler of a city state. He has also encountered the mysterious aliens, the Neighbors, who once inhabited both Blue and Green. Horn next remembers a visit to Nessus, on Urth. At some point, he died. (Or is it dies?) Horn's personality now seemingly inhabits a different body, so that even his sons do not recognize him. And people mistake him for Silk, to whom he now bears a remarkable resemblance.
As Lucius Shepard has written, Wolfe herein "gives us two stories, vivid and brooding, in enigmatic orbit. Jack Vance comes to mind in the poetic exuberance of [Wolfe's] alien worlds, and there are echoes of Borges in the series' puzzle of identity, and of Melville in its somber, penetrating tone. But in this deepening of his masterwork, the voice is Wolfe's own, always deft and dazzling, leading the reader through his wonderfully inventive and evocative narrative maze."