I received this as a Christmas present when I was 12 or so. I remember thinking it was an ok story, but I completely forgot about what happened so it was like reading a new book this time around.
The basic plot of this slim volume is that there's this kid who gets stranded on the colony on Ganymede, one of Jupiter's moons. A plague happens, the colony gets cut off from supplies from Earth, plus there's a mysterious race of aliens hovering around, also.
Some folks say this is a YA novel, but I'm not so sure. It's not marketed as such on the book cover, and although the text is written on a junior high school level, so were a lot of sci-fi stories from the 50s and 60s, when this first appeared. I remember reading a magazine called Analog in HS, a monthly anthology of sci fi stories, and this fits right into the types of stories at that time.
As science fiction, del Rey really had a myopic vision of the future. No personal computers, people still using punch card machines, and bulky early NASA space suits are some of the eye-rolling passages for me. It definitely has not aged well, and the dialog is earnest like those 1950s sci-fi/horror movies that show up on late night tv. There is a fair amount of mild sexism, as the female characters are either domestics, nurses, or are getting into trouble. Not a very advanced society, either. My feeling from the text was that this takes place in the 2050s or so.
I didn't hate it, but I had to force myself to continue reading it. The suspense around the plague is weaksauce, and the protagonists are rather one-dimensional and blah. The mystery with the aliens is predictably solved, and everyone lives happily ever after.
If you have an early teens reader of sci-fi in your house, this might be something worth passing on, provided said reader doesn't mind the dated and unimaginative view of the future. It's not much for adventure, and I would recommend Camus's The Plague for a more thorough treatment of how plague and quarantine affect the psyches of a certain population.