Here is an exciting tale of action and suspense, set in the world of tomorrow. As the story opens, two brothers, Jim and Ken Barry, are traveling by space ship from Earth to a new city on the moon. Aboard the space ship they discover a stowaway, young Dig Allen. Almost at once the three youths are plunged into an adventure that threatens to spell destruction for them all. Dig has set out to find his father, a space scientist who mysteriously disappeared months before. The Barry brothers agree to help Dig. Their search takes them to the "Graveyard of Space" and to Mars. There they meet Old Dorkas, the one person who is able to decipher the last message received from the missing man. Finally, the boys are forced to set out along in an unauthorized space ship. They soon find themselves marooned on a weird, forgotten world at the outer edges of the solar system where unknown to them, their greatest adventure is about to begin!

After bringing the inhabitants to Eros and learning the creature's language through Boyd Allen's amazing new computer that can translate any language and imprint it into the mind, the Space Explorers find that if the creatures are not returned to their planet soon they will die. After finding of their home planet through the use of the Observatory, the two creatures are returned home. Upon arriving at their home planet, however, the Space Explorers discover a band of ruthless men that are burning their cities and capturing hundreds of the creatures. It is up to the Space Explorers to see if they can stop this ruthless band of men and return order to the once peaceful planet.

Dig Allen and the brothers Jim and Kin Barry are sent to Ganymede, one of Jupiter's Moons, to investigate trouble at a colonization project. A desperate race against a gang of criminals who plan to claim Ganymede's fabulous diamond deposits takes the three young Space Explorers on one of their most dangerous assignments.

The swamps and wildlife of Venus are in trouble, and Tim Buckle has come to enlist the Space Explorers to their aid. Trouble arises, however, soon after Tim lands on Mars. A henchman throws him into the chilly Mars Canal—an act which means almost certain death to a man who has spent his life in the swamps of Venus. Dig tries to help him, but the dunking makes Tim go insane. As a result, he and Dig blast off to Venus and leave Ken and Jim stranded. The henchmen who tried to kill Tim take advantage of the situation and convince the other two Space Explorers that Dig has deserted them for being "space Jonas." Their only choice now, he convinces them, is to resign their commission as Space Explorers and throw their lot in with Linton Wells, a rich businessman. Wells wants the two Space Explorers to certify the Venus Kohoolies as being non-intelligent so that he can begin killing them and exporting their skins. Soon both parties are plunged into danger. When a riot stirred up by Linton Wells' henchmen fails to eliminate Dig and Tim, Linton starts a massive manhunt to find them. Jim and Ken soon find out that they have been duped and rejoin Dig—but Linton manages to recapture them. Things take a sudden turn for the worse when Dig, Jim, and Ken are all caught by the Mist Flower and injected with the flower's fatal venom. Their only choice now is to journey to the intelligent Kohoolies' secret city to be treated by their doctors—for the fate of all Venus rests upon them!

Lost City of Uranus is the sixth and last book published in the Dig Allen Space Explorer Adventure series. In this book, the three Space Explorers race after two children who have accidentally launched themselves into space aboard a ship headed to the planet Uranus. Upon landing on Uranus and finding the children, the Space Explorers also discover mysterious, glistening cities under immense sheets of ice.

A book of Joseph Greene's outline notes and sample chapters of the never-published seventh volume in the Dig Allen series, The Sons of Neptune, and other material related to the series.