On Jupiter’s most remote moon Adrastea, or Jupiter Nine, a revolutionary anti-gravity project, known as Agrav, is under investigation—again. This time, the Council of Science has sent their most resourceful troubleshooter, David “Lucky” Starr, and his diminutive sidekick, John Bigman Jones. Though what Bigman lacks in stature, he compensates for in bravery and bravado—a combustible mix that often ignites trouble for the pair.

Upon arrival on Jupiter Nine, Starr and Jones are immediately met with hostility from workers who have been repeatedly questioned and interrogated by government authorities in search of a possible spy from Sirius, an Earth colony settled generations ago that had turned against its planet of origin.

In an attempt to gain an advantage in their search for a possible Sirian infiltrator, Starr brings with him a V-Frog, a small amphibious creature from Venus that possesses remarkable empathic ability. Through this creature, Starr and Bigman hope to determine if the spy is human or automaton.

Unfortunately, an intruder kills the V-Frog in their quarters shortly after their arrival, leaving Starr bereft of his main tool for detection. However, the event raises suspicion that the perpetrator was most likely a robot, for any human that approaches a V-Frog is instantly affected by the animal’s empathic projections of affection and benevolence.

Meanwhile, the Agrav vessel Jovian Moon is ready for test flight to Io, Jupiter’s innermost moon. Against the wishes of Mission Commander Donahue, Starr and Bigman join the expedition, as Starr is confident that the Sirian robot will also be on board—and quite possibly a human saboteur as well!

The question is, will the Jovian Moon successfully complete its round-trip voyage or will all hands meet their doom when the vessel plunges into the heart of Jupiter?

Lucky Starr and Moons of Jupiter conveyed a more sinister tone than its four predecessors. This was the first time in the series that David Starr did not always have the upper hand in every predicament and was, in fact, foiled on multiple occasions both by his own incorrect assumptions—or inexperience—and by the ingenuity of the Sirians. Of course, Bigman’s typical immature and rash antics did little to help the situation, except for a tense anti-gravity brawl at the beginning of the book.

At the time of publication in 1954, the Jovian moon now known as Ananke was called Adrastea (aka Jupiter Nine). In 1975, some of the minor satellites of Jupiter were renamed and Adrastea was assigned to Jupiter XV.

Onto the final volume, Lucky Starr and the Rings of Saturn…