"With only your electronic Compu-Pal, Ting, you must face the deadly dangers of the mysterious planet Volturnus." --from the back cover
Villains of Volturnus, by Jean Blashfield, is one of only three, I believe, EQ books using the Star Frontiers game for its setting. It's the only one of the Star Frontiers books in the series I've read, though I played a heck of a lot of Star Frontiers back in the day.
In this book, you're Kyiki, the son of a mining company president. Dad's company is setting up mineral extraction sites on the world (so it obviously takes place sometime well after the module series), and you're hopping down to the planet with your Vrusk tutor Jak to check out the 'strange new world' that's got the Frontier buzzing. Of course, before you get there there's some sort of problem and you need to abandon ship. Your first choice puts you either all by yourself, or with Jak.
The book is somewhat similar to Pillars of Pentegarn, in that it allows you, in some cases, to double back to earlier points and make new choices. That gives your exploration of Volturnus a bit of a sandboxy feel. Aiding this is that there's not one overriding plot, either. There are three main sets of villains: Sathar agents, space pirates, and traitorous mining employees who are going over to the Sathar side. But you can have quite a few adventures on Volturnus without even running into any of these groups of baddies.
The book does a fair job of showing off the Volturnus flora, fauna, and sentients. The Mechanon don't appear, and the Eorna only through their ruins and abandoned tech here and there, but the Ul-Mor, Edestakai, and Kurabanda are all there. The fact that it does this, however, can kind of ruin the modules if you've never played them. Ms. Blashfield also took a lot of liberty adding in plants and animals that don't appear in the modules because they're not in need of combat stats, which is fine. That adds a new layer to Volturnus that a Ref could use if they wanted.
It falls fairly short of feeling like a Star Frontiers adventure, though. Mostly because you're a kid again. Luckily, your computer sidekick gets lost, taken away from you, or is just switched off a lot. If you end up with Jak, he's a fairly interesting companion--he's sort of an absent minded professor, way to curious for his own, or your, good!
Anyway, your mission in the book is basically just to find a radio so you can call Dad and have him rescue you. There are a few places where you can get into fights (you've got a stun stick, and can find a cache of doze grenades in one path too), but mostly you're running, hiding, or exploring. Nothing wrong with that, but my old group and I played SF heavy on the combat, so maybe that's colored my views.
The artwork of the book is okay. The Elmore cover is not so exciting, but it is somewhat mysterious (showing off a bit of Eorna tech in one of the main branches). The interior art is by Roslof. While he stays fairly true to the way the races and tech are portrayed by Elmore in the Star Frontiers rule books, his pictures here are somewhat hit or miss. Some are nicely done, detailed and evocative. Others seem rushed and kind of bland.
Finally, quite a few endings are truly anti-climactic. There's one where you're climbing a mountain through smoke and fog, think you should turn back, and the next step before you turn around you plunge into the crater of an active volcano... And several are just, "you radio dad, and a few hours later his ship picks you up." In some of the 'good' endings, though, you can save the day by defeating some of Volturnus's villains (or at least calling Dad, telling him where they are, and letting his corporate hired guns--likely your PCs--clean up the mess).
All in all, not the best book in the series, but not the worst, either.
Protagonist: a kid (again) who is at least willing to adventure
Sidekicks: your Compu-Pal Ting who doesn't do much, Jak your tutor, and or an Ul-Mor girl who may befriend you.
Endings: Some interesting, some lackluster (both good and bad).
Art: OK cover (Elmore), hit or miss interiors (Roslof)